Quite frankly, I think the MAINTAINERS file gets a whole lot uglier this way.
There's also a rather fundamental issue: this will likely make people touch the MAINTAINERS file *more*, and from a maintenance standpoint, that is exactly the wrong thing to have (one central file that everybody touches). It just tends to generate unnecessary merge conflicts etc.
(We used to have that issue with the central configuration file, for example).
So the more I look at these things, the more convinced I am that this is not the right thing to do. These things should *not* be in one huge file, and I'd much much rather have the maintainership information be carried along with the subsystem itself, or the files it contains.
In other words, it would be much better to just have per-file markers, along with some per-subdirectory stuff or similar.