The problem with SpaceVim is that it offers a lot of toggles that are easy to switch but there are no examples for more ‘custom’ config and I struggled to figure it out. There’s a lot of examples and guides for nvim so it was easier. I don’t know, maybe it was just me but with SpaceVim I also didn’t really see what’s possible. With nvim I just found long lists of useful plugins that you can add one by one.
As for the future I don’t really worry that there will be next thing after neovim. I didn’t write any custom scripts for it, all I have is just plugins with mostly default settings. It would take me a day to switch to another tool witch is not a big issue.
I think starting with Vim is a good idea. You can easily add plugins one by one when you will see the need for them.