You're basically asking if we can make the ENTIRE game co-op friendly?
As far as I can tell, that would be a no... However, there's no doubting it would be f**king awesome if we could.
However, afaik, the code for normal trainer/wild battles would completely freak out. And there's certainly NO way you could battle together.
I'm also 99% certain that most "normal" actions are illegal in the trading environment, so this is probably a no starter, sadly.
Aside: Thanks for the trading info, could be VERY useful