The XD grip is more ergonomic, and only holds 1 less round compared to the flush fit FNP 14 rounder mag. The FNP slide is much wider than it needs to be, IMHO. I had problems using 200 LSWC's in the FNP. I shoot probably 10K of this type bullet a year in my 45's.
I don't know of anyone that buys a DA/SA to primarily use the DA. I see the DA as an emergency first shot, maybe as a second strike in the unlikely event of a light primer strike. The SA on the FNP is light but creepy, the DA stacks like most every other DA; the XD has a typical striker feel, i.e. mushy and vague.
I find the XD to be very simple and robust in internal construction, more ergonomic, slimmer, as accurate as the FNP, cheaper than the FNP, and mags are easier to find as well. You could conceal the XD; it would be difficult with the FNP. The XD has more aftermarket support than the FNP as well.
Don't get me wrong, the FNP is an excellent weapon, but having owned polymers - Glocks, M&P's, Taurus, FNP, and XD, I prefer the XD.
If the XDm 45 is going to be significantly better than the plain XD, I would wait for one.