I'm a emacs convert from vim (big reason is because module support is just leagues ahead of vim, Vundle, Pathogen, or anything else don't come close to emacs package management). A huge reason why I stuck with it is because evil. evil is very mature and is incredibly close to vim, some say it's a better vim than vim.

I tried a lot of "vi modes" in several IDEs but none of them cut it, you can map anything to evil and you can, of course, map commands to different states. Something I found very usefil is that you can even set states for different buffers, for example, for magit buffers (another amazing emacs module and a very good reason to use emacs) I default those to "insert" mode.

I haven't used Intero myself, but I've yet to find any kind of conflict between evil or any other module.