A very common scenario! Easiest (in my personal opinion) is using Velocity script tokens. You could either 1) create all of the content blocks in a token, then show or hide the section based off of segment values, or 2) I've seen some people use velocity tokens between content section to actually comment out sections that should be hidden for specific segment values. The 2nd option would (I think) allow your users to still edit the content in the Marketo email editor, but you'd basically bookend each section of content with your script token that either adds or doesn't add the <!-- at the start and the --> at the end.
Here's a blog I wrote recently about getting started with Velocity if you've never used it.
Here's a discussion from a while back talking about the second solution I talked about above.
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