Is the new Power Gig guitar also compatible with Rock Band 3

Currently:

What we know:

• Most, if not all, of the legacy catalogue of RB(meaning all the DLC along with the past games) has been charted with the cymbals one uses with the pro drums. If you look at the animations of the drummer in-game, you'll notice that the drummer will play on the cymbals or on the toms on notes of the same color. This is not conjecture based off of that, however; HMX reps confirmed this.
• Everything new with the keyboard and guitar controllers will only be available for RB3 and all forthcoming DLC(from RB3). Same source.
• "There are a lot of cues and “hooks” in [HMX's] authoring flow that have always been there; [they] just haven’t had the software cycles to take advantage of them". Again, same source.
• Harmonix will be re-releasing some old DLC with full support for RB3's new features. Currently they are asking for the community to chime in on which songs they would like to see re-released first.

What we don't know:

• What exactly the cues and "hooks" are aside from the drums. I have, however, noticed in-game that there are times in RB2 when the guitarist and the lead singer will sing together, implying that some of the songs in their legacy catalogue may have support for vocal harmonies in RB3. No concrete evidence, though.

Updated August 16th: HMX will be re-releasing old DLC with full support.

My qualifications: I've used both the RB3 keyboard and a Roland D-50 MIDI Synth with a MIDI adapter.

1. If you use a full-sized midi keyboard in Pro mode, you do NOT use the entire keyboard. RB3 ignores notes played outside the two octave range of the RB3 keyboard. The pro keys chart displayed is the same no matter what kind of keyboard you are using (unlike the pro guitar charts which I understand are different depending on whether you use a 17-fret Mustang or a 22-fret Squier).

2. A normal midi keyboard can also function as a five-button peripheral in non-Pro mode. The only thing missing are the color-coded tags over the C-D-E-F-G keys that the RB3 keyboard has, but since you shouldn't be looking at your hands anyway, that shouldn't matter ;)

3. I don't think RB3 does anything with the velocity-sensitive keys, so you should not lose any functionality if your midi keyboard isn't velocity-sensitive. This is the only answer I'm not 100% positive on (my D-50 has velocity-sensitive keys), but I'm pretty sure.

4. The expression bar on the RB3 keyboard is like the whammy bar on the 5-button guitar controllers - it alters the sound of the notes and when used on a held note with overdrive, it will add to your overdrive bar. My D-50 has a pitch bend joystick that the MIDI adapter converts to the same function.