Interesting, the routes will already start this summer, while the runway lengthening will only be finished before next summer.
Until then they will have a (slight?) capacity restriction on the 5900ft runway of Groningen.
Well surely one destination which would be unaffected by this is London, and iirc, a STN route has been operated previously. Despite the Netherlands having a generally excellent rail network, GRQ is quite out of the way - and a good 2 / 1/2 hours from Schiphol.
Or you can fly GRQ-ABZ-LHR!