I think the ultra small carabiners are probably great to have for long, easier routes with miles long approaches. Any weight reduction is welcomed in those situations. However, in the type of climbing we're more likely to do, easy, timely clipping is important and at times make or break. If the gate doesn't open wide enough to slot the rope without a struggle, the loss of functionality is too big a drawback.

Anyhow, I'd like to see one too. One disadvantage to them may be snagging on each other when racked on your harness (if they are in the open position). In light of that, they may be more fit for sport climbing – otherwise they could snag on even more gear.