Structural regular expressions seem pretty great. If Vis ever gets some Vim features that allow operating across multiple buffers (quickfix et al) I'd probably switch.
I admire Vis but at the end of the day a text editor is just a tool. When the investment into changing out such a tool becomes worth it is entirely user dependent.
[1] https://github.com/martanne/vis#non-goals
[2] https://github.com/martanne/vis/wiki/Differences-from-Vi(m)