Quote from CCCode
Would it be possible to let uploaders create new items with alternatives where we just set the save locations, files and everything else it needs? That way we could just create a new item when one gets added to the game in a patch or add more mod support, etc. I don't know exactly how the customizer works right now so that might be a lot of work, but it would let us add pretty much anything like extended CTM, Random Mobs, snapshot textures and so on.
Oh, and good luck
It would be possible, of course. We had considered doing something like this at some point. I think we worried about massive redundancies and tons of new texture types scaling out of control.
Another thing we've considered is letting texture packs upload optional addons (e.g. you upload a zip of the SkyMod textures/properties, give it a name and then the Customizer includes a checkbox that says "Want to include SkyMod in your pack?"). The reason for doing it that way is that the more customizable mods added onto the customizer, the more bogged down it gets. This latter option would be a simple way of letting developers add mod support without bogging anything down.
Anyway, we may need to do a lot of restructuring with the new 1.5 layout. Neither of the above options are off the table right now.