Kind of OT for this post but I think it would be good if someone could build the what would have to be a lot of bloat and complexity into core and the protocol that would allow a 2nd mempool so to speak that only has 0 fee tx in it. People could still consolidate their small inputs when the main mempool was empty BUT their TX would not be filling up the main mempool. Want to conoldate but don't care when it really happens send a 0 fee with this flag and possibly some pool would pick it up. Would it be worth the program / logic bloat is tough to say but I think it would be nice. Not going to happen, but it would be nice.
-Dave
The mempool on your own node does not mean anything to which transactions will get confirmed, unless you are mining as an entity that decides which transactions get confirmed (you are solo mining, or are running a pool).
A pool's nodes could potentially keep these types of transactions, however, they have little reason to confirm these transactions, even if the mempool has no fee-paying transactions because there is an incremental cost for including an additional transaction by way of having a slightly higher chance the block will get orphaned.