Mostly if it is meant as a SOP for all tools, I would have to suggest against this idea. Three reasons.
One is the rotary joint that allows a through coolant system to even function are wear items, and are costly to buy and replace.
Two – running your high pressure pump which typically supplies the through spindle coolant system is a noisy, power hungry wear item. For everyday all day all tools use is unnecessary, and uses up a lot of system life and energy for little gain. Add in the demister that generally runs with it and you’re talking even more power, wear and maintenance.
Third – thru spindle coolant systems have been known to leak over time and kill built in spindles. Sure.. use it or lose it is certainly relevant here, so if needed I would never-ever hesitate, but in my experience there are a couple three-four tools on any part that need full on chip removal help that could be provided by high pressure through spindle coolant functionality, but the rest not so much.
Just 2, make that 3 cents on the idea.