Well, even with the direct system, applications can do dynamic tracking of users. It should be fairly trivial to listen to blockchain tx of users of your application, track their RC and if people don't transact for a while you decrease the RC delegation and if they transact a lot and are getting close to using it all up, you can delegate a bit more. Unlike HP that has a 5 day cooldown with RC delegations this shouldn't be hard at all.
RE: Direct RC delegations vs RC pools and tentative direct rc delegations spec