The original MX49/MX61 came out in 2012. These new ones have different hardware (so no, there is no firmware update path)
New Feature: class-compliant
The MX BK/BU series features class-compliant, “plug and play” USB audio/MIDI with iOS, Mac and PC. Just plug it in and your MX BK/BU synthesizer becomes your audio and MIDI interface for the rest of your music studio. Monitor all the sounds from your computer via the headphone output of the MX BK/BU or listen to your DAW tracks by connecting the MX BK/BU to external studio monitors or PA gear. The audio converters on the MX BK/BU are made for professional music applications so everything on your computer -- even games -- will sound better when using the MX BK/BU as the output. The MX BK/BU interface is bi-directional for digitally recording your MX BK/BU directly to your computer or iOS device resulting in high-quality audio.
New Feature: FM Essential
"FM Essential" is an FM synthesizer app for iPhone and iPad with real-time synth performance and editing. Connect your iOS device to the Yamaha music synthesizer MX BK/BU, and you can do following:
Play all 271 high-quality Voices consisting of preset sounds from the V50, TX81Z and DX100 Legacy FM PLUS presets and combination Voices specially made for the MX BK/BU series.
Change Voices of FM Essential and control various parameters via the MX BK/BU onboard controllers.
Store your changes
As far as I can tell the MX 2 is pretty much the same as the MX 1 apart from the fact you can now just plug it in and go rather than having to mess about installing drivers.
The wave rom is still the same size at 166mb although there seems to be some confusion over in the USA with some Yamaha "product specialists" saying it has 355mb which is not true.
The FM Essential app is for the MX only at the moment. Your MX 2 unlocks the app. I'm pretty sure that once all the promotion stuff is out of the way, Yamaha will eventually enable the app for the MOXF/XF/Montage etc. I can't see why they would not.
Should have one here soon to test but so far it seems like a pretty good deal for the price.