I really don't see a future for the London City route.
Cork Airport will be lucky to retain FlyBe on the Cardiff route, never mind get them to launch anything else. I'm genuinely surprised that has lasted longer than London City did, as other than a Rugby World Cup related bonus last Autumn, performance has been woeful.
For BA, we have to remember that they are part of IAG and the main thing they are doing is taking higher yield passengers out of the Heathrow aircraft. If that was constantly flying full, it might make some sense, as they could use the capacity there to feed Heathrow long-haul, but that only hits capacity problems for a few summer months.
Maybe if Cityjet acquired Stobart, they could run a twice daily ATR, but the takeover has to actually happen, and even then it needs to be the best use of the ATR. If that did happen, I would be more hoping to see a larger capacity aircraft used for Birmingham and Manchester than London City coming back.