You are assuming that the system (coolant capacity, pack volume, pump capacity, individual cells, etc...) would be able to handle 30kW of direct heating.
A big, assumption, IMO.
Turns out coolant is a good coolant. Let's take a 300 horsepower engine for example, that's ~220kW output. Let's say it runs at 20% thermal efficiency (which would be laughably good), that means the waste heat at full throttle is 880kW. The coolant system in an ICE car deals with that just fine, and that is a big number.
No the only problem with the Tesla is if there is a max delta-T for the batteries that you can't exceed without damage.
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Siemens Installing First Rail Regenerative Braking Supercapacitor Storage in Portland - The Green Optimistic
You could also use regen power to spin up a flywheel storage system, and then use that energy for acceleration when needed.
Kinetic energy recovery system - Wikipedia, the free encyclopedia
We want to add a flywheel do we? Why not just add warp drive?
How I see the TMC designed car: