The WTC has, shockingly (not), been pretty illogical with regards to the valuation of skills like this. It depends on which precedent (or not) they follow. Releases typically get bumped a letter if preceded by a closer-bar circle, but not transitions or non-flight elements, and this is the first flight or release to come from a fwd close-bar circle, IIRC.
Transitions and pirouettes are subject to the ridiculous ‘E’ cap, which this wouldn’t be, but if the WTC thought that an el-grip endo (‘D’) + Ono turn (‘E’) combined wasn’t worthy of more than an ‘E’ (see: Huang, 2011), I see this being rated as low as ‘D’ (if not from el-grip) > as high as ‘E.’
‘F’ seems unlikely, and I’m not sure I’d even want that, considering that would put it in the same class as a Counter-Kim, Nabieva (next quad), Tweddle, and Layout Jaeger. Still a cool skill, and nice to see some originality.