Two examples of contractions in Mandarin vocabulary in common use would be 別 for 不要 and 甭 for 不用. In Edwin Pulleyblank's "An Outline of Classical Chinese Grammar", he suggests that even such a fundamental "building block" character as 非 could be a very early contraction of 不惟.Ah-bin wrote:
Even if they are contractions, the Chinese writing system demands that one character represent a single syllable, so these new characters are a necessary invention if Hokkien is to be written completely in characters.
New characters or new meanings for old characters is not so unusual even in Mandarin. 也 and 都 have nothing to do with their original meanings and 們 is a relatively "new" character, not found in Classical Chinese texts.
This then begs the fundamental question: Should we or should we not, with equal propriety, accept such corresponding contractions and new meaning adoptions in Hokkien, and derive new characters or adapt existing characters for new meanings? There are implications for either choice:
If we choose the more conservative approach of retaining only characters from the classical canon, then:
1. Despite the contractions in the spoken word would still retain their distinctions in written form, i.e. gun for "we" would have to be written as 我人 rather than 阮. The advantage of this is that the etymology is retained (to note that not all sub-dialects of Hokkien use gun as the contraction for gua-lang - Penang Hokkien being an example).
2. There would be no means of writing words of non-Sinitic origin using Chinese characters.
I feel that part of the answer depends on whether we want the end-result of codifying Hokkien to be that the dialect is "locked" or "static" (in the way that Classical/Literary Chinese remained static while the spoken languages evolved and diverged from the written form), or whether we want to allow the written form of Hokkien to evolve the same way written Mandarin has by the creation/adaptation of characters to suit the new usages and contractions over time, per the examples above).
My personal opinion is that using the Mandarin example to justify the 假借字 is not entirely a fair choice. The reason being, Mandarin had the all-important advantage of being chosen and promulgated by the Chinese government as the written standard, so any creation or adoption of characters (be they in Ming/Qing vulgar literature or later) would have had to be accepted by the masses as standard after the May 1919 Movement, anyway. The other dialects do not share such a status in written language, let alone the 'right' to create or adapt characters (Hong Kong would be an exception in this case - though many of the characters used in Hong Kong for Cantonese words are etymologically-incorrect, anyway... but that is a subject for a different forum thread).
So, before I get harangued for going in circles, here is my own conclusion:
Firstly, I have to say that I have a more conservative view of the written language. For this reason, I personally do not condone the contractions and adaptations found in pre-modern Mandarin vulgar literature that - for better or worse - have now made their way into Standard Modern Chinese (e.g. I would not be caught dead using 別 for 不要 - in fact, I always use 勿 for the negative imperative). They fall outside the general canon of Chinese characters that have bridged the various spoken forms of Chinese for 2½ millennia. And for Hokkien and the other dialects (if they so could) to follow suit and derive their own adaptations and contractions would further serve to drive a wedge between the dialects, making them even more as separate languages (in both spoken and written form) than they already are now.
That said, despite the complexity of the various strata of developments of the Southern dialects (e.g. the absorption of the Zhuang and Malayo-Polynesian words), they remain essentially a part of the family of Chinese languages, they have been kept bonded together using Chinese characters for two millennia even as they diverged (Min developed as a dialect around the 1st century CE), and I see little reason for the introduction of Romanisation or other artificialities to fill the gaps, unless it is absolutely necessary.
My conclusion would be that in writing, creations/adaptions for writing in the Hokkien dialect can be allowed, but only when there is absolutely no known way of writing the words using the etymologically-correct Chinese characters for them. I would not put the contractions under this "allowable" category, as one can almost always trace back the original individual "pre-contracted" components (also for the reason stated above, that contractions are sometimes specific to a particular branch of the dialect only), so there is no logical reason to have to create an artificial character for phonetics' sake, but at the expense of intelligibility. That way, when a Beijing native reads a Hokkien text, he/she would have a higher chance of deciphering 伊人 for i-lang/in (contracted) as the 3rd person pronoun, rather than a local contraction such as 亻+因 or something. And when such local creations/adaptations are used, commentaries in fine-print should be added alongside to explain them (in the spirit of the traditional practice as found in old Classical Chinese texts). The nett result is, we still get to write Hokkien using the etymologically-correct characters where possible, and yet intelligibility of the written text is retained - not just for the Hokkien readers, but also to as many Chinese-educated non-Hokkien readers as is feasible - because recourse can ultimately still be made to dictionaries using the Classical Chinese canon.
To me, in the first place, Standard Modern Chinese has already adopted way too many Northern creations that have totally (and, if I may add, imperialistically) alienated the Southern tongues. It would be a shame to make it even more of a mess with the Southern dialects turning the other cheek and doing likewise. Unless and until, of course, we see the day when the "Chinese dialects" as we call them today are officially acknowledged as truly separate languages in the same way that Chinese, Japanese and Korean are separate languages, then everyone is free to do their own thing with Chinese characters. And if that day ever comes, and all the dialects start going ballistic with their own localised character creations (which is part of the reason why today we have a few tens of thousands of characters, the bulk of which are either local creations or obscure variants of the same character), the compilers of the next edition of the 漢韓大辭典 from Korea (at a whopping 60,000 characters encompassing virtually every conceivable use of Chinese characters (and their variants), including all dialects and East Asian languages, this 30-year dictionary project now surpasses the 大漢和辭典 and 漢語大辭典) will have a field day tacking on an extra few hundred more locally-invented, etymologically-incorrect characters for each dialect. Don't get me wrong - I am not against the concept of language evolution. But the Chinese language and its dialects (and here, perhaps we should also include Japanese - having adopted and still actively use Chinese characters) is a unique case for which the complexities involved probably have no direct comparison with the other languages of the world.