Inflation is, imo, not a solution to sustainably fund anything but the security of the network. All possible rewards for creators, engagers, and apps should be from the exchange of STEEM/SBD/SMT between market actors, and not from a "rewards pool" (the whole concept of that is dead in my eyes).

One way or another, trust will be required, that's why I think it is important to also enable users to have a spending account that can be used more liberally without the risk associated with trusting the Active Key of your main account to any apps.