Character terminals were pretty universal. Tek brought graphics. AT&T brought 1Kx1K monitors where apps could be downloaded into the thin client over the serial channel, which could be upgraded to ethernet. They were not truly stateless.
The stateless Sun Workstations provided an amazing workplace environment. Pull the box off of the dock, take the MAC address down for inventory, place the MAC in the server, and it worked when broken out of the box onto a desktop. If the server is booted, everything just paused, and continued where it left off. It was truly stateless. Thousands of developers in a warehouse could be maintained by a part time system administrator. All required management software was bundled. Productivity software like multi-media mail, chat/IM, editing, news, etc. was all bundled. High-end desktop desktop publishing was available. Local disks were not required. Network bandwidth requirements were high and WAN was not feasible.
X Windows offered a great backwards & forwards protocol for thin client computing, it was far superior to dealing with PC's on the desktop, and was in competition to stateless workstations. Maintaining the X Server as the only application on the desktop was fabulous for desktop publishing, trouble ticketing, network & systems management, and web browsing. The protocol was too chatty for WAN connections. Attempts were made with LBX for better WAN performance, state saving for better statelessness, but it was not truly stateless.
The SunRay was a dream come true. It encapsulated both Statelessness and WAN. If the network disconnected, everything was just where it left off upon re-connection. Power-Cycle returned one to a lock screen. Clients lasted practically forever, with keyboards & mice requiring more maintenance. Performance was as fabulous as the server. Multiple web browsers would run for months without ever needing a restart or a crash. Audio & Video were supported. Extremely power efficient. I still use SunRays, even though Oracle eliminated them from their line-up.
I hope for a suitable stateless thin client, in the future. The PC is too thick. IOS was looking fairly stable, but I seem to have issues whenever I do an IOS upgrade now a days. Web Browsers are still somewhat stateful, way too complex, always in need of constant upgrades & patching.
The Netbook concept and Chromebook were good examples of t an internet client, but the software was too thick, making them become obsolete over time, when the hardware was still functional.
I think pervasive internet is offering a good opportunity for a convenient appliance.