I'm a fan of Tiebout sorting and institutional diversity in general; I would like for people moving to an area to have a practical choice of what kind of town and neighborhood they live in, and (for example) for people who want high taxes and high services to be able to live in a town that provides that while people who want low taxes and fewer municipal services to be able to choose that, instead of having towns in an area that have more between-town homogeneity and contentious fights in each town, with few people getting what they actually want. Furthermore, citizens who want to pay high taxes to invest in long-run improvements (better roads, better schools, etc.) should be able to secure those investments from people who might move in and vote for lower taxes, milking the assets (in which the previous residents invested) as they depreciate. To the extent that it's practical, people should get the local governance they want by choosing the town, rather than by changing it.
There are extents, of course, to which it's not practical, or otherwise not desirable. You don't want towns generally to feel they don't have to serve anyone who finds it comparatively easy to move, and a town that is poorly run needs to be ultimately accountable to voters. If the preferences of citizens of a metropolitan area shift, even if you want to continue to have a variety of options, the mix of options will need to change. While it may make sense for the people with less of a practical exit option to carry more weight in shaping how the town changes, you don't want institutional arrangements that lead to no towns in an area serving a large group of people in that area just because those people can move. While I raise this as a warning against too little direct and immediate democratic accountability, it's also a danger of too much direct and immediate democratic accountability; Mayor Curley of Boston seems to have intentionally driven voters who didn't vote for him out of the city and into the suburbs to cement his hold on power. The institutional arrangement should ensure that citizens who are willing and able to move between towns are well-served, while also making it hard enough for them to change the towns that they give serious consideration to voting with their feet and don't remove options for everyone.
In light of these considerations, I'm envisioning a conglomerate metropolitan area, perhaps like London, which has 32 "boroughs" with some variety of institutional arrangements and a fair amount of devolved power, but some centralized power as well. One thought that I have is that the boroughs would have councils with some seats elected by the locals with the least practical exit options (however determined) but additional seats appointed by the central body, which would be elected by voters without regard to exit options. If the population of a borough drops, perhaps the make-up of the local council would be less locally determined; perhaps there would also be some funding tied to population. The hope is that the boroughs would be fairly distinct from each other, and people moving to the area for the first time or relatively able to move from one borough to another would have a variety of attractive options, while making it difficult for them to choose a different borough and try to make it more like those that already exist.
