I'm sure that some folks who remember the old days of Fedora will smile sardonically at the term "Core" here, but Fedora project leader Matthew Miller talked about that in his initial announcement about the ongoing work on Fedora CoreOS: https://fedoramagazine.org/announcing-fedora-coreos/

This reminds me of the JeOS trend a few years back:

https://en.wikipedia.org/wiki/Just_enough_operating_system

I'm wondering what the architectural difference might between an OS meant to be straight up virtualized vs one meant for use in a container.

They say Container Linux (the original CoreOS) will only be maintained for 6 months after Fedora CoreOS is declared stable. I have a few CoreOS instances happily chugging along untouched for 4 or 5 years now. I guess that means I'll have to upgrade them :(

you still have some time as FCOS is still in preview. Also, keep an eye on the documentation that will be offered, such as migration instructions, etc.