getting the software to play nice with such a setup is not currently viable
It has been viable for over a decade. Plenty of groups have done it:
And Microsoft is jumping on the bandwagon:
See the Wiki for more:
Most interesting is Fedora 17 automatically enabling it when appropriate hardware is connected, which should mean RHEL7/CentOS7 will, too.
your $50 tablet is actually a fully-fledged computing device.
Yes, but as a "thick-client" it's a brutally low-end and very limited device. As a thin client, it's a high-end workstation, with huge amounts of memory, unlimited storage, etc.
And if a big market ever developed for thin-clients, you can bet these same tablet manufacturers would come out with even cheaper, stripped-down devices that are only good enough to be used as a thin-client. At what price point would you say it's a good idea? $25? $15? $10?