Even if FFA doesn't have matchmaking, if there's going to be a pre-loaded list of maps for the whole Steam-download-version thing a curated list of good FFA maps is desirable.
(For the record, I once queued for FFA in Starcraft 2 at the height of its popularity. I waited in the queue for 30 minutes only to be placed in a game with 3 people who were clearly friends.
I know what you're thinking - they ganged up on me. Not so. Quite the reverse, in fact... they all instantly resigned. I queued again, got the same three people, they instantly resigned again.
The moral of the story is that FFA is unlikely to ever be sufficiently popular that a matchmaker is a better idea than a custom lobby. Furthermore, I have always found FFA to be more of a social affair, which further pushes one towards custom lobbies.)
tl;dr: I think a ZK FFA matchmaker is not feasible and has significant disadvantages compared to playing them in custom lobbies. Take my opinion with a grain of salt, since in ZK specifically my style does not lend itself very well to FFA so I rarely play them.
