Not sure how much sense these would make here but I would like to:

• - Delay (Time), so that I can change the onset of a modulation
• - Offset (Amount), to make a bipolar source unipolar or generate DC signals for examples.
• - Invert (On/Off), but that might be already possible.

Also, I'm sure your mod sources have limits as far as how long/slow/fast they can be, so having a modifier that lets you extend that would be useful, but I've no idea how you would do that. I don't have much modular experience.