It would be nice to have an attack phase available in the instrument modulation to fade in LFOs. The fade-in should start after delay.
Edit: OOPS… some moderator, move this to R3 suggestions, please. Thanks! 
+1
Although you can achieve this effect with a bit of formula device trickery… See attached
It only works monophonic though so your suggestion would be the best solution.
(Note: it works first time if you load it into instrument 00, otherwise you have to go in and change the linked instrument)
Fading in LFOs is already possible with the current instrument modulations. You just have to set things up in the right order. It’d just be way easier with a single, dedicated parameter.