Zwift let's us create custom zpower curve.

Best cheap solution solution for me = zwift let’s us create custom zpower curve.

If you have a friend with Power Meter you could create an accurate power curve for your trainer.

I agree the feature would be nice but let me just bring up some of the challenges in implementation that the developers would face:

A power curve is not a simple thing.  A power curve is not an offset eg: the power meter says 200watts and zpower says 190 I just need  zpower to be increased by 5%

In reality a power curve would have different offset and gain at different power levels.  I don’t believe Joe Public has the skills or the metrology background to define an accurate curve (citation needed).

Just to add more pain to the equation most power meters are not as accurate as you would expect, however they are extremely precise devices.

Futhermore what about those that would intentionally give themselves a little boost?