Why don't I see tile-based 3D graphics?
This is not really an answer to the latter parts of your question but more to address

As we know, tiles can make it quicker to update large portions of the display at once, as compared with a bitmap. To put, say a letter, on the screen, the Commodore 64 typically does two writes (the screencode and the attribute)

What you are effectively describing is a compressed framebuffer where you are directly writing/storing compressed data and letting the display pipeline decompress on the fly.
I would say that such things &quot;still exist&quot; in today's games/hardware, but not perhaps in form you are expecting.

Compressed frame buffers do still exist. Mobile devices certainly do (for example Imagination/PowerVR have PVRIC, and I believe ARM devices have their own scheme)
These compression schemes are generally &quot;transparent&quot; to the programmer, but it does mean the GPU and display pipeline does less reading and writing of external memory.


A display decompression system like PCG  (Programmable Character Generator) is effectively a precursor to (and effectively a subset of) some texture compression schemes, e.g. such as S3TC/DXT1. In that sense, therefore it still exists, but users don't typically write directly to them, but certainly take advantage of the bandwidth savings.