Cura has it...
I know there is a workaround using the tool change script but it would be way more intuitive (and get faster print times) to set an Active/Standy/Off temperature for each toolhead.
As an example i'm printing key tags for a customer fleet of vehicles where i have to write text with T1 on 3 last top layers. The T0 is used for the "body" of the tag. Right now, S3D heats up both nozzle for the whole part when the T1 is only needed for the last 3 layers. The slicer has the ability to estimate the time until the tool is needed and insert the M104 to bring it to standby and finish off with M109 when the tool is needed.
Again, i could get around it using the variable settings wizard and some scripts... or S3D team could add this function and make it much more user friendly