Probably gonna keep my desktop running win10 by then because I'll hopefully have a new desktop by then that I can easily set up Linux on. Got too much on my desktop to move over and I certainly don't know any tools able to make the process any easier.
Probably gonna just use it as an experimental PC that I can test out server related things on.
I'm adding debian to the drive on a ten plus year old laptop as we speak. It's taking forever because I have to do part of it manually but usually it takes less than an hour and is mostly idiot proof (my current project is on its 3rd week so I am just a special kind of idiot) but a small lightweight distro alongside the windows partition is an easy way to give old hardware new life without migrating data.
I would add a small partition, but I'm always anxious about stuff like that because I seemingly always hear things about windows messing with Linux partitions and breaking dual boot. That, and I am running out of space on my 1TB drive it came with. Two or three years of me using it thinking that I'll never fill it up before I upgrade computers and suddenly I have to worry.