I'd like to see the industry move away from having connectors on the back of the GPU at all and just provide a standard routing interface of some sort. I hate whenever I buy a new GPU having to figure out what adapters I'll need for my multi-monitor setup because my new GPU has different numbers of HDMI and DP outputs than my old one.
This seems unlikely to happen for the foreseeable future - if ever. As pixel counts grow the port standards are evolving quickly (both HDMI and DisplayPort).
A machine where the display interface is on the motherboard will have a hard time keeping up with these developments, whereas keeping the interface on the GPU will allow the user to add support for new standards over time (see: HDR, 8K, etc).
But then you are limited by the number of connectors on your motherboard. I know people who have more cards to support more monitors(not in SLI, just side by side)
