Incorporating a Jail Plugin, so that when players break blocks or do things bad in towns, they would be sent to the nearest Jail. Commands could be like...

/jail [player] [Jail] [jail cell number] [time in jail (minutes)]

/unjail [player]

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To setup a jail you would select a plot

/plot active

/jail create

Players that go outside the plot would be teleported back into the jail

To create a cell on the block you are standing on (would detect in which Jail it is based on the plot):

/jail cell create [Cell Number]

There would be a sign on top of a door saying the cell number and who is in there and what time they have left..

[Jail]
Cell #4
medemi68
3 Minutes

to set it up you would put,
[Jail]
{Cell Name}

You use the phrase "break blocks or do things bad in towns"- This is kind of vague. I assume you just mean "when they do bad stuff, they get jailed."

So, we have to define "bad." Just defining it clearly enough that we could actually implement auto-jailing is bad enough, but any algorithm like this would be based on heuristics. At that point, this starts to sound more like a feature out of an anti-cheat or anti-grief plugin.

So, probably the best we could feasibly do is allow mayors or assistants to jail people. So we just need to work out a jail system. At this point, though, we're barely different from the many jail plugins out there- and any MCTowns jail commands would just be wrappers around the jail plugin's commands.

So, while it might make it slightly more convenient for server owners to set up permissions for jails (in that they would only have to make the player a mayor, rather than give them the permission node), this doesn't seem like it brings a lot feature-wise. I'd rather just have server admins configure jail plugins, rather than devote dev time to wrapping their commands.

TLDR: automatically detecting "griefing" or "bad things" isn't feasible and is out of scope of the project, and so this seems like it'd just be gluing a jail plugin's functionality to MCTowns' commands, which seems like a waste of dev time.