I grew up in a house with 8 bathrooms, a tv room, 3 living rooms, 7 bedrooms (grandparents never got on and had separate bedrooms) but still shared with my sister until university..one room was my parent's study, one spare room was a toy room, another room was a guest room. My mum who shared a bed with 6 siblings didn't see it as strange nor did my father who shared a room with his brother until he married. They thought it was important i learn to share and it served me quite well cos i coped fine with sharing a 3 bed London terraced with dh's 3 sisters, his mum and dh after i graduated from university which is what enabled us to start our careers and buy our London flat without my dad having to buy our house for us.
It was a big room though and we had desks and wardrobes. When I came to the UK to study, I hated having my own room.. I think privacy is a very western concept perhaps borne out of post war prosperity. In my home country we became prosperous roughly in the 1980s so our parents still have memories of far more cramped living conditions and don't see anything wrong with it.
The uk is getting poorer though so i am not sure hanging onto these expectations from more prosperous times is so practical unless we completely change our system. I even saw a rightmove ad where someone who got bought her own london flat in Bloomsbury actually lived in it all the way until she had two children sharing the tiny room in bunk beds. If the rich have to do that, what do we expect the poor to do.
In any city or semi desirable town post 2030, I expect the poor to live in one room, the middle income (two civil servants or two teachers) to rent two bed flats, bankers and software developers (without family money) to own 2 bed flats or two bed terraces in less desirable towns or up north (for those who can work remotely) and for the truly desirable housing (victorian terraces in London/SE and semis with 3-4 bedrooms) to be for the hedge fund managers, traders or those with family money. As the old die off their inheritance would be consumed in end of life costs and care home fees so eventually the equity in their homes will be whittled down and then further split between the descendants.