You are an incredible mystery hound good sir.
Solus' version of iscan did not work but maybe it could. I am ahead of you by 30 minutes as I've tossed myself at the dev team again about the 650. (Normal is 10 paces behind, so may this be a trend🙂.)
Epson's version of iscan, which you quote, I compiled from Epson and began to install, yesterday, but missing run dep called cxxtest or something. It's a weird gtk dep and I could not find an equivalency--which is moot as you just discovered no 650.
I agree with you 100%. If kind devs could re-tool utsushi or the iscan for the V series plug-in we'd be in business.
The eopkg with a cd command installed like butter. But I never got my hopes up! Yes the seth uploader had a grand plan, if limited in scope.
I was hoping the future was here already with open source hardware like scanners/printers/peripherals but it's not.