They'll monetize the hell out of BL3, but as long as the core gameplay remains the same I don't care. If they sell skins for the vault hunters, or even sell something equivalent to golden keys I don't mind one bit. If they have legendaries that can only be obtained through buying them I'll be extremely pissed. We already know they're going to have a ton of DLC like they did with 2, that's pretty much a given. The one thing that will really piss me off, and it's not even related to monetization, is if they make bosses one time encounters again like they did with several of the bosses in TPS. Farming bosses is core to the Borderlands experience. That's an absolute must.
I also don't want anything equivalent to the grinder either. Borderlands is not about crafting, it's about that moment of excitement when the gun you've been farming finally drops. There's still a level of excitement with the grinder, but it's not the same.