I've thought about this from time to time. There are some cons but overall gentrification is an excellent step forward for a city/society, the main problem with gentrified cities is that the poor people who can't afford anymore lose their houses and therefore, become homeless - or have to move somewhere else where they can stay or have family members that can give them a roof. In theory, if many cities around the world were gentrified it would be a much better place as it would decrease crime, poverty and trashy cities. Again, the issue here would also be the original residents whom would happen to be poor would be left without a roof and unemployed people couldn't afford to live there anymore. Not to mention that senior retired people sometimes barely have enough for the essentials. The solution? Make an exception for the residents who have lived there all their life, or at the very least, apply an increase but one that wouldn't leave them ruined. Gentrifying cities is a wonderful Utopian concept but as we all know, those that are hungry with power and money just don't give a crap about those who can't afford -- Well, not totally. If it were a family member (who they didn't have any issues with) they would be given a pass. And lastly, the worst case scenario that could happen for a gentrified city - The poor and criminals would gang up against the new residents to banish them out because they feel they "own" the city as they were there before them.