YABU
No one needs to have a £million mortgage - there are always options. No one HAS to live in an expensive area. Areas get expensive because they are so popular and pleasant to live in that demand outstrips supply and prices go up.
YABU to say that "no one" can afford a £500pm increase - obviously most people can't, but while there are people paying at least £1400 per child per month for private school fees, and plenty of people saying elsewhere on mumsnet that "I could afford private school but choose not to" there are clearly plenty of people who can easily shoulder that kind of increase - you may not realise quite how rich some people are.
What the government should do is invest in building houses and stimulating growth in valuable and rewarding employment businesses in areas which haven't experienced such house-price inflation, get people moving out of those hotspots to cheaper areas (including making sure there are jobs to move to) and creating a thriving and growing economy that works for the whole country not just the wealthy hotspots.
And absolutely no to subsidising the people who have over-borrowed and have created financial trouble for themselves.
We have been told for YEARS that the low interest rates are temporary, that they will be going up sooner or later, and that we should make sure that our borrowing will be robust in the event of sharp interest rate rises. This is not news. 6 years ago when rearranging my mortgage after a previous deal ended, I put plans in place for how we would cope with a jump to 6%, because that was the sensible thing to do, and there were plenty of articles in financial pages saying that interest rises would happen sooner or later. We didn't move to a larger house, despite the banks being willing to lend us enough to do so, because I knew that if we did the inevitable hike in interest rates would be more difficult to deal with. I'm glad I did that obviously, though this house is getting pretty cramped now DC in teenage years. But this is a free country, people are allowed to make their own decisions and take risks, and it was fair and reasonable for other people to make their own decisions and gamble their future financial stability rather than being cautious and choosing lower-risk options. Whilst that's their right, it is also their responsibility to shoulder the consequences and it would be totally wrong for those who took a lower risk decision to insulate the risk-takers from the consequences of their decisions. Which is what would happen with any of these "other ways" you allude to.
They aren't going to be left homeless, they can sell up and still have some equity, and can make their housing arrangements according to their actual means rather than aspirationally commiting to pay for a lifestyle they can't afford and then wanting other people to bail them out when it goes wrong.