I've not heard anything recently.
Turkish has been expanding aggressively in recent years with BRS thought by some to be the next likely recipient because there is no direct Middle East connectivity from south west Britain with the smaller Turkish Airlines aircraft to Turkey likely to be a better fit commercially and operationally than the larger aircraft used by the MEB3.
The ubiquitous Simon Calder gave the rumour legs in a piece in his newspaper at the beginning of this year.
Perhaps a more realistic appreciation of the situation was put by anno aero in a feature about BRS last year which can be accessed via this link:
Bristol Airport set to hit 6m passengers again; easyJet rules the roost
The BRS routes director told anno aero at that time, “We work very hard to match the right airline to the right route. We are not in the business of encouraging new routes which are not sustainable for our airline partners, so we will sometimes sacrifice short term gain in favour of finding the right fit.”
anno aero believed then that the airport might turn to Turkish Airlines if the operational performance challenges proved too great for the MEB3 to overcome.
Realistically then Turkish seems far more likely than an MEB3 future presence but the timescale is hard to estimate.
Ryanair
Many thanks for your thoughts EI-BUD and FRatSTN.