GSM said that they were continuing Tenerife into the summer base operation, which means it should be bookable.
Part of the reason for Eastern Airways' success is if a route is not performing to expectations they won't keep it any longer than they have to, and they definitely won't wait for the route to 'settle in'. They've chopped routes a thousand times because of this so I'd say the BRU route is in grave danger. I've heard on numerous occasions that Eastern's fares aren't cheap either, which is probably half the reason the route has got poor loads.
Regards.