I'm also having this issue where i'm trying to change the svg fill of the logo but can't because prismic forces me to use an <img>
The error I get (which I'm sure will be the same for everyone)
This is the third client project I've run into this issue on this year (3/3) so at least for me it's a pretty common request
Logos and icons are very likely to sit over varying coloured sections (whether that be website themes or just changing background colours) and uploading multiple variants to accommodate different styles is very impractical, while keeping these all in code is very unfriendly for clients to edit.