Does anyone else arrange their data in a way that protects against the inevitability of a windows install failing??

No…I arrange it against the potential of the OS install failing. No OS is infallible or immune to you or some bad other thing happening. I wouldn’t put my data on the same partition of a Linux install either- I wouldn’t put it on the same disk even, if I could avoid it, just like on Windows. If for no other reason than historically, having all your stuff on the same disk as the OS could cause really significant performance impacts. It’s less of an issue with solid state storage, but it’s still there, to say nothing of storage density of hard disks vs solid state.

Plus, depending on what you are doing, it’s very possible that your OS disk is the most active one in your system, so it’s going to potentially have wear related problems much sooner than your data disks.

Did you have a point you were making?

what to immediately nuke

This scenario is the one that you have to approach differently than the others. The only way to approach with this scenario and be reasonable sure it’ll go the way you want, is to have the default state be inaccessible. i.e. everything that you want to be “nuked” has to be already in an encrypted state that only you are able to access. This way, the nuked state is the default state if you aren’t around to grant access.

X can be an abstract FTP like server which uses rclone instead a file system. Or can be a web server that uses rclone

You literally just listed 2 ways to do exactly what you are asking. Why would those not work?

Ohhh…are you not mounting the remote? You know you can do that right, mount an rclone remote? If you mount the remote, it’ll just show up as a file path to your system, and you can just serve it via whatever server you like.

The trick here might be if you are running under Windows, getting other user accounts/system services to have access to things can take some fiddling, depending on how you set things up.