I'm sure Rhino envelope generators must have been discussed here many times before. My opinion is, while the EGs are very flexible and offer a lot of possibility, it can be overkill in some cases, especially when a user just wants to do a quick exploration on certain combination of sounds. I think we can improve that in one of a few ways, which could potentially encourage users to start out simple and get deeper when desired.
1. Allow users to switch between EG modes (perhaps by a single button on the EG window): the advanced (current EGs) and the classic (ADSR-ish). The classic EGs offer knobs/sliders which are MIDI learnable, and have default values of A, D, R at 0 and S at maximum. Each oscillator can have different type of EGs, and can be switched back and forth. Better yet, when the user has done with the classic EG and wants to get deeper, the advanced EG can imitate the current value of the classic EG and the user can further from there. Or,
2. With the current EGs, allow users to move all the EG points in SUSTAIN (highlighted) area (up, down, left, or right) simultaneously by holding SHIFT or CTRL while dragging. It could work like a drawing program, where holding, say, CTRL key while dragging will move all the selected points at the same time, and holding also the SHIFT key will reduce the degree of freedom to either vertically or horizontally. With this, I think it can be made to work basically like classic EGs.
Any MIDI controllable aspect for each of the EG points or a set of points (besides time stretch which is already very nice) is, I think, also a very welcome addition.
I hope either of these options could be a good addition to this already very good synth.
Poonna