2D is just a special case of 3D with very boring matrices. The "2D acceleration" in older chips tended to mean acceleration of the Windows GDI functions, whereas at least "3D acceleration" is more generally applicable stuff.
AMD/ATI do make a chip with no 3D features, they sell it for inclusion in rack servers which they rightly theorise will be connected to an LCD panel for maybe 5 minutes if they're being installed by someone who is new to the business and doesn't have a reliable network based auto-installer yet. It has basically the same framebuffer setup and so on as their 3D chips, just no 3D. I would not be surprised to discover that this is actually just as expensive to make, and is done purely because 3D drivers are notoriously complicated, therefore unreliable and no-one wants their web server crashed with an Oops message saying the 3D rendering engine lost an interrupt. Not providing the hardware is a 100% effective way to prevent people installing unreliable 3D drivers on their server.
If you're able to convince business PC makers that these framebuffer-only chips are the Right Thing for corporate desktops, you may be onto something. But I suspect that with e.g. Excel and Powerpoint already taking advantage of the 3D acceleration, you won't get much traction.