FRA should do well, even without an LH code on it. Traffic will still be able to interline and sites like Expedia will sell itineraries on LH but with an EI connecting flight.
I think Scandinavia could work and would be a potentially a strong inbound route. SK's CRJ900s could be a good fit - at least to begin with, although that would limit the number of low fares. I doubt we will see a Scandinavian route from Aer Lingus, they are very weak in Scandinavia - they fly to HEL a few times a week, in summer - thats it!
Much more likely to see someone like Norwegian come from Scandinavia than Aer Lingus.