Same for the AF lounge

As far as I'm concerned, the only good thing about more competition is that there may be more MFU opportunities and perhaps lower prices on BA

As for Delta flying into LHR - as there aren't any good onward connections within Europe on ST partners (except CDG and AMS, which are already served by direct flights), I'd guess they would mainly attract US-originated passengers going to London. I have serious doubts (as others have) that their business model will work for any others considering the product offered vs. the competition.