⭐ Merited by ETFbitcoin (1)
Just a quick question: is this just for mainline client dev, or are we alternative developers allowed to ask questions too? 
You'd have to ask Gavin to be 100% sure, but I think that anybody working on software that deals with the bitcoin network should be welcome...I think they should, too. The list should be about discussing the protocol evolutions, not only C++ code for this particular client.
As many pointed out, it's problematic that there is only one client. As in any internet protocol, the protocol itself should be very well described, in a formal way, so that multiple implementations may exist. This is all for the health of Bitcoin. That's why I think the list should encourage generic protocol discussions, and alternative software development.