It's absolutely the case that poor residents get priced out and do not necessarily benefit from a neighbourhood becoming hip.

The cool new retail is tangentially to blame through second order effects, but the real problem is the inflexibility of the system in responding to change which results in a shortage of housing, which means that the disruptive impact on low income persons is really severe as they have no where to move to when things become more expensive or they are evicted.

Much like how the solution to increasing retail rents is more flexibility in retail zoning, so to is the solution for increasing rents.

It's less of a big deal if a cheap lame neighbourhood suddenly becomes cool if you can easily bail out because there's plenty of affordable apartments elsewhere. The problem we're in is that there's a general shortage and so in many places, losing a long held apartment is like an existential crisis because everywhere else is even more expensive and there's a shortage.

Another approach is that in redeveloping "cool" areas we could increase land/property taxes and developer fees so as to recapture the land lift and divert toward public realm projects that benefit existing long time residents. The area becoming cool and getting new condos pays for the new pool and new below market housing.

Should be mentioned as an aside that the actions themselves of poor people can ultimately gentrify a neighbourhood just as much as retail. A neighbourhood can become known for a vibrant arts/music scene that ultimately gentrifies it not just because it has some bars, but because the working artist residents are they themselves creating the attracting works in putting on events and shows. They earn a meagre income as working artists but ultimately may displace themselves as condos come advertising themselves on the scene that they've created.

Cyclical neighbourhood change I think is inevitable so I think what we really need to focus on is not necessarily finding ways to keep neighbourhoods the same, but giving people and retailers options so that when change happens, it's not disruptive and painful.