Any idea if this would also apply to miles that I have with CX (as I could transfer my MR points)?
Or would this only apply to miles that I have with BA's FT program?
Not being particularly familiar with BA Executive Club or CX Asia Miles, I can't comment too much. However, the BA forum seems to claim that a roundtrip UK-US MFU from WT+ (even discount fare basis T) is 25,000 BA miles. Of course, earning 25,000 BA miles is pretty tough unless you tend to fly either premium (WT+ or better) or short-notice (Y,B,H) fares.
The deal isn't so good with CX Asia Miles for BA upgrades, from what I can see.