My feeling is that BRP Essentials will be more like CoC than RQ when it eventually arrives. The core CoC system (without magic, monsters, etc.) can be easily distilled into a small number of pages.
As for your choice, Mythras Imperative provides a nice base for a modern/sci-fi game. Also, OpenQuest (an OGL game so you can base your own stuff on it without a license) is a possibility. It's based on MRQ1 but is much simpler than Mythras. There are fewer skills, three combat skills (ranged, close combat, unarmed) and no hit locations. OQ seems to try and create a hybrid of the classic BRP games published by Games Workshop: RuneQuest 2nd Edition, Stormbringer 3rd Edition, and the 96 page GW RuneQuest 3rd Edition core book. I like it a lot but I prefer simpler iterations of BRP like CoC and Stormbringer.
I see a lot of threads about Mythras/RQ6 which seems to be a popular BRP choice at the moment. Also, the games based on MRQ1 (of which Mythras is one) are all largely similar (and similar to BRP) so it can be easily ported to other variants.