I wanted to turn my old cheap server into something more usable, and ended up nearly replacing every single part to create a tiny server + gaming PC in set-top-box form. I had the 980 ti as a retired card, so this was a great opportunity to give it some more life. I plan to hook this box up to the living room TV to use for gaming (both modern and likely old console emulation), as well as to run game servers for friends. I haven't yet decided if I want to run windows 10 (leveraging the excellent Windows Subsystem for Linux for remote administration) or just go straight linux and run games through Steam's Proton or in-home streaming, but I love that both of those options exist. And with a 1 TB M.2 SSD I have room to dual boot if I can't decide.
I definitely had a lot of trouble getting the parts to all cooperate, going through multiple itx motherboard/ram combinations, but finally found that the MSI B450I worked with some ram I already had kicking around. The MSI motherboard I got was NOT ryzen 3000 ready, so I needed to pick up a cheap Ryzen 3 2200g ($60) to run the bios update.