Emulating a TMS9918A with an FPGA isn't very difficult as long as you don't want composite video output. I did it maybe 8 years ago with VGA, works great. Not much use for it, but it works great. I added some of the features from the later V9938/V9958 MSX video chips, such as the palette registers, just for fun. You need an external video DAC of some kind; I used a semi-vintage ADV7120 I think--not sure, it's been a long time. Suggest you shoot for 800x600 SVGA; it works out to have the right aspect ratio and border size. I've seen some less-than-thought-through implementations using 640x480 that have a stupid-wide border region.