MAINT: Drop support for PySurfer + mayavi?

Now that:

1. Brain / PyVista / PyVistaQt has begun to mature;
2. PyVista backend has good notebook support;
3. mayavi has gone even more unmaintained than usual (I have had a PR open for 3 months that fixes some bugs on latest vtk that hasn’t been reviewed yet); and
4. PySurfer isn’t too actively developed anymore

I propose that it’s time that we drop support for it, as it lowers our maintenance burden: deprecate for 0.24, and in 0.25 remove the mayavi backend. We can leave the set_3d_backend infrastructure in place for future compatibility in case we want to migrate to a different 3D backend in the (probably distant) future.

I figured I’d ping @GuillaumeFavelier and @agramfort first since you’ve primarily been guiding the PyVista efforts. If you’re on board, I’ll ping the rest of the MNE steering committee since I think this is a potentially large enough change to warrant bothering everyone.

[agramfort]

yes +1

but I’d like to kill this bird with the new coreg GUI so we’re done for good.

[prabhuramachandran]

@larsoner – thanks for the response. I agree with your analysis. And yes, this is a real problem. A major problem for me is that this has been the status for 20 years, bulk of the work has fallen on me and it has become harder and harder to find time or motivation. That said, I still think that it is a useful project. Another issue for me personally is that I have an almost “Debian stable” mentality and never update my Python environments for fear of breaking stuff so tend to live in my own cocoon – that is the only way I can get my work done at all. What I am going to do going forward is to put in a little time each week on Mayavi maintenance and the first goal is to work with some folks at Enthought to ensure that the CI is working and notifies us of issues. I will take care of the core issues that I seem to be the only one comfortable with and others will help with setting up CI and other things that they are more comfortable managing. Hopefully together this should be better. Anyway, am hoping to do a better job. Thank you @larsoner for all your help these last few years and your patience.