There have been a lot of work done on MQTT HA integration
Pull requests · openhab/openhab-addons · GitHub
One thing I’m already missing though on the page, mentioned in my linked to above previous, is MQTT device_tracker
especially useful for auto-discovered automatic home/away statuses for Tiles, Nuts, iPhones, Apple Watches, AirPods, BM2 vehicles, Bosch Nyon **eBike computers and many other devices.
That’s what I meant with full HA MQTT discovery support for OH5 in my original post here 
But it is definitely an improvement from the last time I tried it with the initial OH4 release, so I’kll give it another test run sometime soon.