Actually, if you wanted to automate it after the export, you'd have to strip out this part:
<span style="background-color: rgb(255, 250, 165);-evernote-highlight:true;">
Then, you'd need to strip out the closing \span tag. Actually, it doesn't seem like it'd be that hard if you were good at scripting. i think it could be done with Automator but i'm more of a designer and know only enough coding to be dangerous. The challenge is that Evernote's export is a bloated mess of HTML.
i'd really like to see something like this myself to bring highlighted text into Roam. i just need each highlight on a separate line.
Maybe if Evernote would let me replace their highlighter app with Liner or another highlighting plugin, we could do it. (?)