Except it doesn't quite work like that does it?
There isn't an issue with people not selling their homes, there's an issue with what purchasers of adjacent lots to those homes and allowed replace the previous homes with and we're not talking about incremental changes to front, rear and side yards, we're talking about not having to provide off-street parking and not having adequate garbage and recycling options etc.
What's taking place is insensitive - if not inappropriate - building form and use. It's no different than allowing someone to put a warehouse in the middle of an existing residential neighbourhood and justifying on the basis of the city not having enough light industrial/distribution space.
Sure, but that's not a question of being
forced out of your home; it's a question of finding that your home no longer has all the attributes you once found desirable, be that sunlight for gardening, ample street parking, the perception of privacy, etc. It's best if we can satisfy the preferences of as many people as possible, but in some cases you can't. There's a balance to be found, and we can quibble about what it is, but I don't think there's any reason to see the preferences of existing homeowners in an area as a
trump card over those who would like to live in inner-city neighborhoods, but can't due to their current lack of stock and consequent unaffordability. To go down that route would mean a continuation of the trends we've already seen: the aging and hollowing-out of inner city neighborhoods, the closure of schools, etc. etc.
Personally, when I walk around a neighborhood like McKernan-Belgravia and I look at all the anti-infill signs, I really can't see what people are objecting to. No doubt there are some really bad, insensitive infills, but I also think there's a lot of catastrophizing about this topic.
If housing is unaffordable, it's better to remedy that situation on the demand side, not the supply side. What's needed is an increase in the incomes of those who can't afford housing noting that this also means they can't afford food or clothing or transportation or education or medical or dental care and they still won't be able to afford those things if they're provided with "affordable housing". If that needs a universal basic income or something similar, so be it. It's also worth noting that a UBI is transportable so that people can take advantage of jobs or training or educational opportunities that they wouldn't otherwise be able to do because they' can't afford to relocate and give up their subsidized housing and they can't afford to commute from their subsidized housing to those opportunities.
Subsidizing the demand side has been tried a million times all over the world and is a consistent failure as a long-term solution (conceding that there may be a limited place for policies like rent control). If there's too little housing for the number of people, no amount of giving would-be buyers money or tax breaks will allow them to fit; it just drives up prices. UBI might be a fine approach to other problems, but it doesn't fix this one.