I guess markets such as HUY, MME, LPL or NWI, mabye even CWL, only justify a single hub link demand-wise. And that is covered by KLM. HUY had AF for a short time, MME had limited hub-feed by BD into LHR, but realistically, these airports are one network carrier airports.
Choices for Lufthansa are therefore limited. They will have to focus on developing BRS, ABZ, LBA and GLA (and maybe BFS/BHD once it looses the LHR link by BD). Lufthansa has already tried GLA and BRS unsuccessfully, and those two were probably more promising than ABZ and LBA.
The interesting question is whether they should go for FRA, MUC or DUS as the hub they could feed from there. While DUS has a much more limited connectivity, it has a lot of P2P traffic from British regional airports (lots of flights from MAN, BHX, NCL). MUC is the most convenient airport airport for connections, but from the UK, it is quite a bit out of the way for connections to Northern and Western Europe and the US.