The closest analogue to what you described in the ARM world would be plugging either a Computer-on-Module or System-on-Chip into a carrier board. Today's ARM deployments are presently largely focused on energy efficiency, so they make heavier use of integration than typical x86 deployments.
e.g. https://www.toradex.com/computer-on-modules/apalis-arm-famil... https://www.toradex.com/support/partner-network/hardware https://www.toradex.com/products/carrier-board
> Also until you can run non-linux "desktop software" on one, it will always feel like a "tablet"
There are millions of linux users around the world that would challenge your assertion that desktop linux doesn't qualify as anything beyond a tablet. In any event, Windows already runs on ARM and some rapscallions have already got it up and running on a Raspberry Pi despite Microsoft's present prohibition on doing so. I'm sure Microsoft will free up the licensing in due time as market demand presents itself (if only to allow interoperability with M1 Mac VMs).