If it's about length only, why not simply create a Macro with Musical Functions > Length > Set all to: 1/16 and tie it to a KC?
This way you can simply select the part or events, hit the KC, and all your drum hits will be 1/16th (also after overdub, those 1/16th already stay 1/16th).
That being said, I would not mind seeing input quantize length ;)