Something I’ve never checked for but…are there any linux installers that run from within windows? Shrink the windows partition, create a linux partition, populate it, install grub, and tell the user to reboot and choose linux? I think general lack of good ext4 fs support in windows might make things difficult, but you don’t actually need to do that part from within windows. There could be a second installer that’s triggered the first time they boot from grub.
I feel like a well supported installer like that would dramatically lower the barrier to entry. It could make dual booting windows a breeze for anyone who knows how to run an installer and reboot, which is what people actually want.