Surely there are enough people with a serious, technical interest in FAI and related topics (and I don't just mean among LW regulars) to make such a channel sustainable.

Vast majority of IRC channels are ghost towns, with virtually no activity after the initial burst. You will have to achieve some critical mass to make a channel viable. Be prepared to announce and give periodic seminars and champion the channel in other ways if you want it to live. And yeah, ##FAI is the way to name it.