I think it's a good sign that BMR are being quite active and assertive in going looking for routes with potential. I'd be more concerned if they'd picked a bunch of routes and then stubbornly stuck with them even though they weren't growing.
The Nordics make a lot of sense as a point of expansion outside the UK. I think it's quite smart. It fits in the range of the ERJs, and the maint base at ABZ. Northern Europe is a fist fight between EZY and FR at the bottom of the market and BA/LH/KL/AF further up. If you haven't got a sponsor (as BM have with LH out of BRS), it's perilous territory.
By comparison, there's lots of money floating around the energy business in the Nordic region. (Look at SK running GOT-IAH direct in an all-business configuration). DY don't do regional flying, so there's no immediate LCC risk. I think it's good to see them hopping equipment around markets, looking for demand.
The only reason BM should be considering new equipment is to lower the ASK cost, and that only makes sense when LFs are sufficiently high and robust. They're not there yet.
Having flown BRS-FRA/MUC a few times since the LH codeshare kicked in, LFs are noticeably higher. I've a worrying niggle that LH are screwing BM on rev-shares, but given that fares are still quite high, it seems to demonstrate that given access to good sales channels and hubs, the model is working.