I think hazbird's idea of speeding up activity token production is very interesting; the activity tokens take a rather long time to get as it is, and we're talking about items that can be 500+ tokens.
I'm not sure if 'create havoc in the economy' are the words that I would use, but it would probably affect the economy in ways that some would like/dislike. I think it is probably best to steer clear of any options that have risks, and you're right PvP tokens are just fine coming in at the steady rate that they are.
Anything that is not sellable would probably be the best bet... this implies new items or ones similar to the ones already in the hard to obtain activity token reward token pool. A large increase in activity tokens seems like a really convenient way to do it, but maybe most players would rather have activity tokens be a separate thing.