I think it adds a complication. If we’re not arguing about mixed content being possible, then it’s a matter of what is more practical.
Obviously behind what a user might see, alsorts could occur.
A user’s browser not understanding to highlight safe: as a url, unfortunate ways?.. call that trivial perhaps but perhaps call it an irritant to devs and users who will wonder what they are looking at.
Clearnet devs might be referencing http:// and safe: in ways that confuse supporting software?
I don’t know all the issues that forcing safe: might throw… but the point is that I wonder, neither does anyone else. Given that there’s a simple option to be flexible with default use of .safenet and enhances use as safe:, I don’t see an advantage to not doing that.