A poster well connected to BRS mentioned this on another aviation website a week or so ago and said the aircraft would be CRJ 900s. However, no reason was given for the flights. I can't imagine they are other than charter flights for some organisation(s)or other.
bmi regional
The first Hamburg flight operated today. According to the BRS press release "thousands of bookings (have been) made since the route was announced earlier this year" . Doesn't indicate how many thousand but let's hope they and future bookings will generate a decent yield.
The bmi regional CEO is quoted in the press release: "...................we are currently reviewing other opportunities with the team at Bristol Airport and hope to announce additional routes in the months ahead".
Perhaps not quite so immediate as the remarks the airline's CEO made when the route (and FRA route) was announced in December when he said, “We are also reviewing other opportunities with the team at Bristol Airport and hope to announce additional routes in the new year.”
bmi regional takes off with new Bristol to Hamburg route – Bristol Airport
Brussels Airlines
According to posts in the Newcastle Airport thread the SN NCL-BRU, currently operated by a Flybe DH-8-400 in SN livery as on the BRS-BRU route, will cease at the end of the current winter and is no longer bookable afterwards.
Currently the BRS-BRU route is still bookable for the coming summer. However, it carried slightly fewer passengers in 2011 than its NCL counterpart and almost certainly did so again in 2012 so the obvious question arises. We don't know yields of course so that might be the key.