Dubstep was in no way an offshoot of grime. Dubstep and grime were developing around the same time, in fact dubstep was finding its roots before anything really grimey had taken place.
Secondly, Trimbal isn’t a name for the collaboration of James Blake and Trim, Trimbal is the long version of Trim. It has nothing to do with James Blake. Harmonimix is the alias James Blake is operating under on this track.
Finally although you are correct in saying that James Blake hasn’t made much intense, dark, urban music, I wouldn’t say it’s fair to brand his music collectively as ‘cerebral electronic pop’, because his music varies a lot. His 2010 catalogue is a perfect example. That’s why I don’t agree with your statement that it’s a great surprise to see him working with Trim, because James Blake is an artist who likes to change up what he’s doing.
Excuse the rant, I just felt obligated.