Such a feature would be great. But equally important would be the possibility to have different tax rates depending on the customer’s location. Pricing plans are typically for digital goods. You can often sell such goods to foreign countries at a lower / no tax rate while you have to charge domestic customers the regular rate.
At the moment, you can only define ONE tax rate for ALL pricing plans. It would already be a major improvement i you could set ONE tax rate for EUCH pricing plan INDIVIDUALLY.
Then you can build workarounds and sell / show only certain pricing plans (with the associated tay rate) to specific clients.