Behind the scenes Evernote notes are 'just' HTML files. With KaTeX they could add LaTeX-like math notation into Evernote without much hassle: https://github.com/Khan/KaTeX It is even under a permissive license!!
To see how reliable and easy it is, just try out the Electron-based note app 'Joplin', which uses Markdown for general formatting + KaTeX for math notes: https://github.com/laurent22/joplin
And it allows the import of Evernote notes, syncing over multiple services and has a web clipper.