Tag mode, maaaybe, after all known bugs are fixed and all nice features I can think of have been added.
Team, not happening, ever. I don't feel like going into detail, but anything involving more than 2 people as players is much more challenging to implement and would require a complete overhaul of the entire networking model. As for '2 players + CPU' or whatever, I don't really feel it's worth the effort given the CPU level (and team mode being already iffy to begin with). But that would be less technically unreasonable -- someone else could possibly do it if there's enough demand (though I would certainly not count on it)