4 a day EMB would ruin the route.
I cant see that happening the BD1 on Monday had 126 in flex economy and 18 in economy, Tuesday had 112 in Flex and 24 in Econ so either way that will stay an airbus as it surely produces results.
BD1 always does well as its departs before BA and pax will pay the flex fares. Its the mid morning and afternoon rotations that are killing the route.
It has been 7 rotations recently when EDI is 6. If it goes down to 6 and with new routes like BASEL connecting via LHR (rather than LCY) and Tripoli it may just (only just) save it from being doomed forever.
Its a catch 22 - reduce service (take away full service for non frequent fliers) = lose some pax, reduce service further (take away food for frequent flyers in economy) = lose some pax, drop routes (AMS, BRU, CDG, TLV, Kiev etc) lose more pax, drop frequency, lose more pax.
The increase in service for full fare economy has probably won back some pax from BA but only on the commuter routes.
They need to keep frequency, increase the product offering in economy (a refreshment would be a start), improve lounge offering (how costly are soup, fresh bread, maybe sandwiches to provide), launch more routes (which they are working on) and they should get the pax back.