The version on Github still should be working. It’s a Python plugin that attempts to replace the functionality of the old docker, yes.
Right now Krita has Reference Images Tool. It has some shortcomings, but at least it doesn’t crash 
And it has some nice things about it too: How to snap square brush marks to a grid - #7 by Dluogs
There are feature requests to for example pin the reference images to view so it doesn’t zoom, rotate and pan together with the image, but stays on top (like the old docker did). There is one student for Google Summer of Code that made a proposal for this. For now students hasn’t been selected yet, on May 17 it will be know if this student has been selected for the program and will be working on that, or not.
But the feature that David Revoy is missing is somewhat on the TODO list. And if you just want to use reference images, the current Reference Image Tool is already nice and very usable.