It may become necessary to implement DDS textures like Homeworld 2 uses. One of many reasons to update to DX9.
Compressed textures work just fine on DX8. And I think DX7, for the matter.
So what options are there? I mean the latest games (UT2K3, Battlefield1942, Freelancer, Starlancer (I think)) have multi-maps but are much more efficient at this stage. And if things are going to be done it might be better to start now before it becomes a problem down the road....
I'm pretty sure none of those games use more than two maps simultaneously (Though I'm not sure about BF1942) - even UT2k3 doesn't use a gloss map like FS2Open does.
Only the next crop of games (Namely, HL2 and Doom 3, and games based on their engines) will use more maps, and they'll require at least DX7-class hardware (And in Doom's case, use specific extensions, like register combiners, to squeeze much closer to PS1.1 capabilities for hard-coded effects even for those cards). It's just that multiple textures are inherently much slower, which is exactly why they aren't commonly used.