I think it's fine as is, with the Lounge being used for non-Macs.
Although the NeXTs share a few things in common with Macs, they clearly are not Macs. True, we do stray from the 68K theme sometimes with discussions of PPC Macs, but they're getting to the point where they're getting to be quite antiquated. Think about it--the 68KMLA was founded in 2001, just five years after the last 68K was discontinued. We'll be coming up on five years for the discontinuation of the PPC next year. Also, there is no solid PPC forum online--PPCMLA is deserted, as many have said. I also think it's fine to have the subforum for Apple II/III/Lisa discussions, since they are Apple products (and are also OLD Apple products, going with the theme of the site).
Personally, I think this is just a bit of changing times. I've been a member here for four years. PPCs were just being discontinued when I joined and at the time nobody really thought of them as "old". However, a lot has changed since then--Apple dropped support for them in the operating system, most of us have upgraded to Intel Macs, G3 iMacs are gaining popularity as collector's computers, and there are fewer 68Ks still standing. We can certainly keep the focus on 68Ks, but I think we'll see more PPC discussions for these reasons. And no, I see no reason to change the forum name--Radio Shack is still Radio Shack despite now selling TVs and other equipment in addition to radios and radio parts.
However, the NeXT systems are completely different animals altogether. We're comparing Apples (literally!) and oranges here. In reality, it's no different than adding Amiga, IBM, HP, Commodore, or any other brand to the site. Pretty soon we'll have forums for each brand of computer, the TI calculators, Atari VCS, GameBoy Advance, you name it. I'm against the creation of NeXT subforums for this reason.
I think we should stick with Apples for the actual forums and discuss anything unrelated (NeXT, IBM, etc) in the Lounge--just like we do now. Of course, it's fine if non-Apples come up in an example such as networking on one of the Mac forums, but an actual discussion about a particular feature in NeXT Step would need to be a Lounge topic.
Just two cents from an oldtimer on the forums...