Yes, I'd be happy to make the changes. What does that look like
logistically? Sending patches to this mailing list asking for review?
(Sorry, I know this must be explained somewhere but I haven't done much
research about how to contribute to Emacs yet.)

I don't have a copyright assignment yet, but some kind folks are educating
me about how to procure it over at the icomplete-vertical repo.

https://github.com/oantolin/icomplete-vertical/issues/14

As an aside, have you tried non-fido icomplete? There is one simple change
that makes it infinitely better in my opinion: fido forces a
completion-style choice on you, icomplete gives you freedom to choose for
yourself! (I shouldn't say so because I'm the author but I love the
orderless completion-style: https://github.com/oantolin/orderless.)