Hello Muhammad,
as I first heard about the discussion of the establishment of an egyptian arabic wikipedia I find the situation is quite similar to the discussion two years ago, as the first minor chinase language wikipedia was about to start. So I think maybe the experience we had in the chinese language wikipedias can help you a little. Though, this is my personnal impression, it is not representative and if surely do not match the standards of an academic research (indeed I would find such a research helpful and interesting).
Before the first minor chinese language wikipedia was started there was a long during (I believe at least one year or more) discussion inside the by that time chinese community. The arguments exchanged by that time (for or against) are very similar to the arguments that are now put up in the arabic community. I personnaly took at that time a skeptic view against a new chinese wikipedia. My concern at that time was mainly of the division of the community.
Now, after more than two and a half years, we have seven chinese language wikipedias, these are zh (the standard chinese, mandarin), zh-yue (cantonese the first minor chinese language wikipedia established in march 2006), wuu, cdo (min-dong-language), gan, hak (hak-ka language) and the zh-classic (the classic language). Except the zh-classic all other languages have native speakers, some have established writing system, some not.
For me personally, after two and half a year of experience, the most important conclusion is that my original faer of a splitting of the community proved to be wrong. Especially the yue-language wikipedia developped well. It is a small (far more smaller than zh) community, but it is a vivid and sustainable community, with a lot of interchanges between zh and zh-yue communities. I find this interchange very fruitful. We have articles originally in zh-wp transfered to zh-yue-wp and vice versa. I think the creation of this language version very beneficial.
Not so well do the wuu and gan wp develop. Both languages suffer from being endangered, their native speakers diminishing rapidly and they have no really established writing system. Also after the lifting of the ban on mainland-china these two versions remain crankly.
Personnally I am especially disappointed by the hak-ka version wp. I think it should do better as it is now. But naturally, the number of Hak-ka native speakers are less than yue, wuu and gan.
So, I think that a writing system, especially a used writing system is also important. Yue has such a system and the system is very popularly used in BBSes, blogs and chatrooms in Hongkong. I think this is a vital point for the success of the yue-wk.
My friend Theodoranian said while the discussion two or three years ago, the big community should not be afraid that the minor community would splitt it. Contrary, the big community should help the minor communities. I am very happy that the time proved him right.
Ting