Australia

This is a good article

TLDR:

Super funds already calculate your change in value of super assets, but not the taxable income on an individual basis, therefore the current proposal is minimally burdensome compared to only taxing realised gains

What FUD.

It's bugger-all work to slap those calcs together. The ledgers are already unitised at member level and it's only a couple of function calls to calculate unrealised gains for a given period.

Even for defined benefit funds, you can pull quotes at two different dates to calculate gains with very little effort.

That's absurd. Reporting super details to the government for 80,000 Australians would not be a significant ongoing cost for any competent provider.

There would be an initial cost to develop the reports, the ongoing cost would be minimal as it would be spread across the existing costs to maintain their reporting infrastructure.

If somehow this is true for some super providers, you should avoid those providers as they are already operating with incredible inefficiency.

I do wonder how it would work for those in defined benefit schemes, but I doubt any of those are above the $3m threshold.