@burnme I understand very well what you talk about. And i agree that a application doing the math you need would be helpful in your case ... but thats nothing to build in wallet. The walllet provides a interface for such kind of 3rd party apps, delivering all information needed. (http://localhost:8125/test)
In your case you should maybe define exactly what you need and find a developer programming it for you, if you just have to handle one country tax law and you have access to burst price in your tax currency by transaction timestamp ... it is not that big deal to plot out a excel sheet for a specific burst account. Writing a general app that fits the need of all and all special cases is much harder.
The whole aspect you describe will be a big issue in the future ... tax and crypto just don't work together very well, as crypto is not bound to identity like fiat ... a lot of current laws just don't work with crypto. It is quite amusing, if i pass a border, i may only take a given amount of cash with me. But considering that crypto is cash, and i have my 'private keys' with me, i break the law, every time i cross a border. I have accepted that i'm a money launderer and terrorist for the authorities ... hope you find a way to not get criminalized by reporting every single crypto transaction with all related data, like timestamp, exchange price in fiat, source/recipient ID etc. ;-)