I could be wrong, but i seem to remember player skins are pretty
small, about the size of an average webpage jpg. I don't
think that would be much to download at the time that you
connect to a server.
A pack would be a pain for 56k'ers to download, but as is the
way with any software you download over a 56k modem.
Maybe the pack could be optional, the real goal is to have
a gta3 realism expansion that's standardized across the
board, not to force everybody to use it.
As for the invisible skin, i have not seen this, but if it's just
a skin, I'd bet it's pretty easy to detect on the client side.
I'm gonna go look at what mods are out there.