Hmm, I hadn't really thought about it in detail. I'd say let's keep it to actual products and information about those. Therefore, lets avoid articles about people and companies. However, products by those companies you mentioned would be fine. I would say we're going for less of an encyclopaedia and more of an 68k information archive.
I don't know how far we want to deviate from 68k Macs. I'd say Apple ][ and other vintage Apple products are good. NeXT, however, is a bit more removed, but I don't see any reason not to include it if someone really wants to.
Of course, all this is just my thoughts on the matter -- I'd love to hear everybody else's!