I love mine I've had it over 2 years. It was a first-gen DIY Framework 13 and I ran into a faulty fan early on. I worked with their tech support and they sent a replacement fan under warranty. Took 5 minutes to put it in and all parts inside have QR codes that take you to the marketplace for replacements and repair instructions.
They do have official Linux support for Ubuntu and Fedora. I can attest to Linux Mint working well on it although I don't use the fingerprint reader, which I've read has some issues on some distros.
As for upgradability, I've not needed to yet but you can just order a new motherboard and any other parts off their marketplace and drop it straight in. Should take around 20 minutes or so. I suspect this would take longer on the 16 since it is more complex.
Also, here is a link to the marketplace if you want to browse the parts. I think you could build one from scratch from here, but I think it would cost more that way. https://frame.work/marketplace
At least if still downloads them you can edit them out if it's something you want to save.