It would also strengthen Star Alliance in the UK as it is clearly the weakest airline grouping here at present.
Not really a strategic worry, LH, OS, LX etc all feed their European hubs from the UK and even UNITED have more flights out of LHR than FRA. Each alliance doesn't need to have a based carrier in every market, that's the whole point of the alliance, to feed their hubs via spokes.
AF/KL is arguably Delta though the back door.
<insert your own joke here>