The proposal is presented as a "Q&A site for non-native & native Arabic Language learners, linguists & experts to discuss finer points of the language."
One can very well discuss finer points of the Arabic language and grammar even in transliteration as long as one uses a proper transliteration system. One just needs to have a brief look at scientific papers in English, French, or German about Arabic language, grammar, and literature. They have been discussing grammar and technical things about the Arabic language for decades and centuries and had to resort to transliteration because it was difficult (and presumably expensive) to typeset their academic work with Arabic characters alongside Latin ones.
My point is that as long as a user obeys some rules and knows how to transliterate properly, there is no reason why questions on this site should not contain Arabic in transliteration. I am talking about "proper" transliteration, because false and unclear transliteration can make a question unintelligible, thus defeating the idea of a Q&A-site.
Regarding your example question: The transliteration of رسول as "rasool" is not scientific. But even so, the transliteration in your example question is well enough that it becomes clear what it is you are asking, so that I could give you an answer.
Something else: The one who answers the question is not bound to use transliteration, too, just because the one who asked the question used transliteration.
Finally, I myself will employ transliteration and I know how to transliterate Arabic properly on a scientific level. And yes, I am committed to support a Q&A-site that discusses "finer points" of the Arabic language.