I've already done as much as I can to keep the community from being divided when the expansion comes out -- the unified binary system, continuing support for those who don't buy the expansions, the pretty generous trial system for the expansions, etc.
One thing I can't do is give away copies of the expansion for free for those people who don't feel like paying for it but still want to play it, which is essentially what you're suggesting, in the end. Because only about 50% of the expansion ships are those which are bonus starting ships, the rest of everything is capturables, or new AI types, or ships that the AI uses, or new map types, or whatever. Having those things on would presumably be a must in order to really get to the crux of what you're asking, and that becomes something where it's just giving away the expansion free to the secondary person.
Aside from that, players that don't download the expansion (or expansion trial) separately once the official release comes out won't have the requisite images to show those ships, anyway. Those would then just show up as pink squares.
I always hate to say no to requests, but this is the sort of thing that I just can't do. The way the expansion works as far as with players who do and don't have it goes, is pretty set at this point. There's simply no way to get around groups of players who want to play together with different expansions of the game aside from the solution already put in place -- simply disable the extra expansions that all don't have, if everyone doesn't want to add them.