Umm, what do you mean "which is still surprisingly a P&S" ?
Lens upgrades? It's a fixed lens and I think the P90 has no filter threads either - so no filter or wide/tele adaptors.
There is also no hot-shoe so no flashes can be mounted either. I think there's no PC socket either so no external flashed can be connected that way either.
So for P90 accessories I think you're limited to straps and cases. I'm also not sure why you're impressed with this model. The P90 is fairly unimpressive as P&S "Bridge" cameras go.