A bit alarmist to think this is likely to happen.
It is occuring elsewhere and the position of western countries is getting worse each year. Deficits continue which means that government debt continues to rise toward historic levels.
Pensions offer an easy way out for bankrupt governments whether by further financial repression (taxation) or a more explicit stealth theft.
Although they will sell it as your assets being 'invested' it will be no more than swapping any long term pension assets (stocks, bonds, commodities, property) as held in ones pension (or group pension) to be replaced with devalued government debt.
i.e. swapping long term assets to fund short term government funding.
There are various countries out there which have either made a full grab or are considering a partial grab in the form of forcing public sector or private group pensions into funding government liabilities in all but name. The last grab would be private individual pensions but even this should be considered.
In my view a pension now includes added risk that is both difficult to price and difficult to hedge against. For this reason I see paying off a mortgage as a better place for any spare cash (on the principle that one's primary residence is the last / most difficult asset to force financial repression on).
The rules of investing during the golden decades now need reviewing IMO.