Outrun style road demo MSX2

Looks great. Probably I don't add nothing relevant but in order to make the MSX2 version more viable, how about adapting the game context to a suitable scenario than the opposite? I mean the game argument should be located in a desert or similar environment where the problem of sprites should be less problematic I think. Yes, this maybe is not your goal but at least can be a solution. Personally I wouldn't mind having a game like that.

On the other hand, is your engine able to implement elements such as mountains or clouds on the horizon/sky?

In other words: Hyper Rally with hills, that's what I've predicted pages ago... ^_^ On MSX2 you'll end up with a better looking Hyper Rally. For more landscape features, you'll end up with a V9990, and possibly an R800.

But, we'll see.

I want an unusual Dodge Charger out of road !!

Maybe, my idea was to use line interrupts to swap among tilesets and to "train" each tileset for represent all the possible views of the road a given range of distances. This can be done using vector quantization and e.g. k-means clustering.

You could sample the positions of the line interrupts on the Y (on the screen plane)

If you sample the positions of the line interrupts on the Y, e.g. each 2 lines, you have to decide which tileset to show in each vertical band 2x256 accordingly to the distance of the road seen in the band and the screen plane. Tiles should be trained to show two lines of screen. They should fit a tileset of 256 positions even without vector quantization. Each time you call the line interrupt you need to update up to 32 bytes in the PNT, because the same tile number in the two tilesets has different meanings. You should double buffer PNTs for this (up to 4 buffers if you sample Y each 2 lines).
Each line you should also swap the color table to allow moving lines on the road and replicate, in a SW manner, the complexity of screen 4 in the offroad objects (same as Bifrost or Nirvana on ZX spectrum, but guided by the line interrupts).

In theory you could also sample the positions of line interrupts on the Z (distance between the screen plane and the point on the road segment). I think that in this way you get quickly a mess. I would avoid this solution.
In both cases you keep representing the same distance used during training the tilesets even when hills or pits appear.

Anyway, if you want to compete with vespertino on the size and color of items off road this solution (one FG color each two lines in a 8x8 tile) could be too limited.

Screen 1 has only 4 sprites per line and limited colours though.