Even if the current engine can not handle the extra notation for cymbals, I think it would be forward thinking to at least have place holders to allow charters to place cymbals ... which could later on be represented with the ho/po notation currently used for guitars.
And if this is possible, I think it would be highly probable that there would be those in the charting community that would rechart all your DLC/songs to date with proper cymbal usage ... quite likely even for free. With the peer review that you are proposing, I'm sure the quality would be quite high. No one wants to make a mistake in front of the other charters.
Heck, you might even add to your revenue stream ... I for one would pay a bit to rebuy an updated version with cymbal charts.
Thanks for consideration