I think (but I have not tested) that if you can use the DeDRM plugins to import your books into Calibre… You might be able to use Calibre’s conversion function to make them all ePubs (which are Kobo friendly). I don’t have a Kindle but I do use a Kobo and have had to run DeDRM and some conversions to make books compatible.
Good luck!
Ya… I’m with you 100%. It really feels like commercial software is the “minimum viable product” rather than a complete and quality piece of software. I’ve opted for FOSS solutions wherever possible for me and it has worked out swimmingly. Only place I’m still struggling is my home PC. Making the jump to Linux and potentially risking game compatibility is still a bit of a hurdle for me, but once my Win10 license loses support, Linux will be a very strong contender for my main OS.