The problem is more or less devices that do not support dns challenges or only support letsencrypt and not the acme protocol (to chain acme servers, etc)
What kind of devices are you thinking of? Like switches and other network gear?
I've deployed LE on IPMI (dell, supermicro), so that's not a good excuse ! As long as you have a way to "script" something on your devices (via ssh, API or whatever) .. you are good to go
FortiGate 50g (higher version than 7.0 probably fixes that, but no idea when that will be released), some synology nas and there are tons of other boxes like that.