I am strongly for allowing dialects of Arabic as subjects of queries.
I think it is bad policy to start a stackexchange community by ostracizing those who want to write in some dialect. Well understood in the Arabic world everybody *writes* in MSA, but also everybody *speaks* in dialect, all Arabs live in some "dialectal" environment, and foreigners travelling in the Arabic world have to deal with dialects. IMHO this is reason enough for useful questions about dialects to be raised and answered. And sometimes the best way of formulating a question about dialect, is in the dialect itself.I believe that one should let people write in (and care about) whatever form of Arabic they want (MSA or dialect, written in Arabic script or some transliteration) as long as they tag their question properly as concerning (or being written in) a specific dialect. And time will show whether the community will tend to be MSA-only, or rather dialectal, or both.
After all, you can not evacuate the fact that every native Arabic speaker alsonecessarily speaks at least one dialect, and that this dialect may be much more important than MSA for him/her in his/her daily life. And dialects make Arabic culture richer, they should not be considered as a "necessary evil" or as a "handicap", as some MSA-purists do consider them.
The other solution is to consider renaming the community into "Modern Standard Arabic Language" so that misunderstandings are avoided.