16 bit Graphics Chip
Well, one obvious choice would be to use the chip that the Yamaha devices you mention were extended clones of, the TMS9918.  They're not manufactured any more but can be acquired with relative ease if you look in the right places, so are definitely a plausible choice.  The TMS9918 was used in the first 16-bit personal computer, the TI-99/4, so you'd be in good company there. 
 You'd lose a bit of resolution versus the MSX, but it's still a pretty reasonable system.

Another choice would be the Motorola 6845, which was somewhat less advanced but a lot more versatile -- it ended being used as the basis for the IBM PC graphics cards up to and including EGA (and is present in backwards-compatible form in the VGA too), so is capable enough for real work.

Edited to add:

The NEC uPD7220 is another good candidate, or more particularly its 16-bit successor the uPD72120.  Unlike the 6845 this implements a command-based system where you tell the chip what to draw and it updates the video memory for you.  Like the 99x8 chips, it is designed to have its own memory that it manages access to (whereas the 6845 is agnostic about whether the memory it's connected to is its own or managed by the host CPU: it only generates addresses and expects external circuitry to perform the actual memory access) and provides a way of requesting changes to the memory from the CPU along with general drawing primitives (but unlike the 99x8 it provides a bus request/acknowledge protocol that allows direct access to it too, and is able to use a standard DMA protocol to perform block transfers to and from system memory).

Like the others above, it's an obsolete part no longer manufactured, but can be purchased on ebay and similar sites.