For a crash cart, you can pick up a vga capable display at your local thrift store for $20. The specs barely matter, it just needs to work enough to get the network management back online.
At least on the crash carts I've used, the displays were always VGA. Not sure if that's still the case. I'm not sure why.
If I was building a crash cart today (without knowing the environment) I'd have at least VGA, DVI, HDMI, and DisplayPort as options. It wouldn't be too difficult to get a monitor or setup (adapters) to support them all, especially if one just needs to buy a couple for the datacenter or whatever.
Its not like you need 144Hz 4K to troubleshoot a server - its a good enough defacto standard.