I read some where that Lufthansa do not get on with Loganair for what ever reason. That would explain the reason why the German routes not taken up from BRS. Perhaps the German routes are only viable with a Lufty code share.
FRA and MUC might only be viable with a LH codeshare or by LH itself, although it's been suggested elsewhere that part of the problem with the flybmi/LH code share from BRS was the likelihood that LH got more out of it than flybmi in terms of yield.
History tells us that there is a market for FRA, especially when it's part of a hub service there. Unfortunately, the market might not be big enough for something of, say, A319 size at the frequency needed to make a service realistic for passengers, many of whom would want to use the route to access FRA for onward co-ordinated travel.
About once a year the management of bmir/flybmi would announce that they were looking at sourcing larger aircraft for some of their routes with BRS-FRA quoted as an example.
70-80 seat aircraft might be the optimum size for the market for a 3 x daily BRS-FRA linked to LH onward connectivity, but how viable that would be in terms of yield and whether such aircraft would be available might be different matters.
I imagine that the BRS management is still trying to get some form of LH return to their airport, at least to FRA, but only time will tell if they succeed.
I wouldn't be surprised if eventually Easyjet launch Munich but Frankfurt would probably need Lufthansa.
easyJet only seems to operate from Frankfurt to Berlin Tegel which no doubt is one of the routes they picked up when they took on Air Berlin's services from Tegel. easyJet does have a larger presence at Munich, with their UK routes being LGW. LTN, STN, MAN and EDI.
Whether a p2p easyJet route from BRS to MUC would be viable remains to be seen. In recent years easyJet has surprised me with some of the routes they've started at BRS, most of which seem to be working out for them, if loads and commitment from the airline are guides. Who would have thought, for example, that Catania would become a year-round route?