The first people to get displaced by upzones are the ones who can't afford to continue to live there after a place gets redeveloped. I think this is really the key - you can "save" the castro, the painted ladies, and the billionaire estates in cow hollow, but you need to give people living in upzoned areas a 1-1 swap. The housing that gets built needs to be AFFORDABLE, and the people that would be displaced if they turned Excelsior into towers can't wait 10 years for rents to come down.
So here's an equitable solution that requires too much money/effort/organization/faith:
* Raise land taxes on the millionaires and billionaires in the mansions and areas that don't get upzoned - you can't have your cake and eat it too
* Everyone in the area of an upzone gets their rent frozen, and gets to move into a new "equivalent" apartment as new ones are built - in the same neighborhood. Rent is unfrozen when the median rent price lowers back to where their rent is now, or equal difference between median and theirs at freeze time.
* Govt pays market rate for the housing out of land taxes - city-wide rent control for up-zoned communities, in order to move into new places.
* Create a special economic zone in some of the upzoned communities - prioritize building and reducing regulations like sight-lines, and people in that community get first dibs at new housing (with their rent subsidies, or if buying a new place).
* Flurry of building occurs, eventually excess is made and maybe prices go down, but the buildings are less of a soulless shell for rich people, formed off the remains of the community that was once there, but filled with people who've lived there.