Okay, I checked one out today. It's fun to play around with, but the limited polyphony and also the limited controlability via a MIDI keyboard (the FM doesn't respond to velocity or mod wheel) pretty much determine its use in conjunction with the sequencer. What is nice is that you can automate almost all parameters and that you can use the arpeggiator in combination with the sequencer, which is a feature I'd like to see in many more products. The warp function of the sequencer is also neat if you want to move towards odd rhythms instantly.
If you want to program FM sounds in an oldschool way, this won't be much easier than on the DX7 though. So it makes FM a bit more accessible, but only to play around with and hence on a surface, not really in depth. The intentional programming will still appear cumbersome to most I guess. When it was announced I thought I was sold on it. Now I'm glad I tried it out first. Although I don't have any current linear FM devices in my setup (wink, wink, Pro 2 update?), I don't think this would add enough new and significant sonic variety to justify its purchase. So I'll pass.
If nothing else in this direction comes up, I'd rather consider getting an original DX7 again at some point.