I'm actually not against changing the indexation mechanism for the state pension - so long as it continues to genuinely track inflation.
We've seen how the triple lock ratchets, as pay rises typically lag the inflation rise by at least a year - so the state pension doubles up the inflationary increases. That was deliberate - to increase the pension over time- but it isn't sustainable forever.
If we no longer want to deliberately increase the state pension in real terms, it would make sense to flatten the increases over eg 5 years - ie every year you increase the pension by the average of 1/5 inflation or 1/5 average salary change. It does mean the pension lags inflation a bit, but over time it's stable.
Our state pension is now reasonably similar to the non-contributory pillars of most European countries' state pensions. And that's effectively what our state pension is - since it's a flat pension and NI stamps are awarded not only for work but also for being on benefits and SAH parenting.
Other countries often additionally have a contribution-based pillar, where you get out in proportion to what you paid in. They effectively behave like our workplace pensions, just administered by the state. We do need to improve workplace pension take-up. Perhaps by making personal/workplace pension contributions mandatory at a given % of income. The UK pension system actually gives us much more freedom to choose than many other countries (a real UK strength) - but unfortunately too many people choose not to contribute enough, which isn't sustainable when the state has to pick up the slack in their later life.
What I think absolutely can't happen is abruptly making the state pension means-tested. I genuinely think that would bring about the collapse of the social/welfare model in the UK.
What I fear would be possible - but utterly morally bankrupt - would be to stop indexing the state pension against inflation, which would effectively make it means tested over a few decades (down to £2-3k per year equivalent in about 40 years). I think that would bring about very harmful behaviour change, but not immediate system collapse.
Wonder what the socialists will do...