Macs have really thin profiles on most of their devices. So they will not be upgrading to anything really good as they have no way of cooling a fast graphics card properly. Plus they prefer quiet machines, so even if they could, they wouldn't because the small fan would be really noisy and there is no space for a bigger and quieter fan.
So a lot would have to change for better graphics to happen. Since it is unlikely Macs would grow thicker, then I don't see any improvement in the near future. Maybe the iMacs would be improved, since the 5K model really needs a lot of power.
The new 15 inch MacBooks have a Intel graphics only option because for some things it is almost as fast as discrete graphics. I could see Apple dropping discrete graphics eventually once Intel improves a bit more. Maybe 2-3 years. This would avoid the bad solder issue on some models, where the graphics card became so hot that it disordered itself.
So essentially no chance.