I love this scenario. No matter what Ash will do with them, there is always going to be a group of fans who dislike he decision.
If he keeps them through the DP saga, people will get bored and will want him to gain new, possibly more interesting pokémon, during his extended travels. If he drops them off at Oak's, we'll get complaints about him never using them again (Sceptile would cause the most uproar I'd imagine). And if he releases them...well, thats self-explanitory. Cue the 'Ash is a crap trainer' rubbish
Personally, I'd rather have him gradually desposit each pokémon in favour of a newer candidate ie. Johto. He'll then gain a new squad to tinker around with, at the same time still having his strongest team at his disposal.
THIS time however, there would be more rotating going on. That way, everyone will get a fair share of battle experience.