I perceive that there is a lot of interest in 'other caliber' AR's and that is a market that is worth pursuing. There's a buck to be made here, so why not offer what your buyers want?
I'll tell you what I'd like to see: a .45ACP conversion! I'd bet it would be popular. Mags may be a bit of a problem, but not much of one.
I see that there is a potentially profitable market for the following 'other' calibers:
A lot of shooters (like me) are picky about their equipment. If it doesn't have a horse or a snake on it, I don't want it. So Bushmaster needs to consider providing what I want to buy, or I'll have to take my business to those who DO provide what I want.
I'm telling you I WOULD buy a .45 kit from Bushmaster if it was available and at a reasonable price. But that's a sale Bushmaster will never make if they don't make the kit.