The Formula boards have always been well featured mainstream overclocking boards. The Rampage seem to be the best for those using sub zero cooling. Both tend to come out later - I suppose Asus spends more time getting them just right.
Edit: Oh, duh, you were talking about the Asrock Formula
And the Rampage Extreme is already out, but no word on an Asus
Formula yet
Yes after the ASRock X99 OC formula, rumor that it will release this Saturday the 13th in Japan.
As for ASUS and the Rampage Extreme.
Only single M.2 implementation. (Asrock OC Formula dual M.2 x 4 (3.0 and 2.0)
I don't need wifi, (Asrock OC Formula has mPCIe slot so can add your own, more flexible)
I don't need the gimmicky OC Panel, (WTF)
I don't see a future for SATA Express (M.2 is minimum of 2 x better)
For me the Asrock board is the better option, and should be cheaper as not paying for features i will not use.