However sweet the deal, it's not gonna happen IMHO. It makes no sense at all. WX is getting hammered on the EDI-LCY route and BA found the A318 too heavy/uneconomical for it's own operation compared to the E-Jet/CRJ. If they then also try to avoid the BA 318 timings they will miss the peak LCY inbound times for sure, making again, no sense.
Can you imagine an A318 in the WX scheme!
(sorry but that's the spotter in me talking...)