There is of course, as has been mentioned before, Liverpool to Nottingham, where one could form them up to the maximum length of principal stations on route. I believe the most constraining platform is Manchester Oxford Road Platform 3, using the already fitted SDO at less major stations on route.
One could re-form the fleet up to a number of six car units, I believe one could get up to 12 of them, 8 if we've made the remainder all be 5 car (as per the other thread).
I would think there are some other routes that could take four car 222s, longer distance, nice to be comfy but not needing massively high capacity routes, 17 trains would be a fair few to find services for with EMR but... Other DMUs aren't forthcoming at the moment.
And in terms of Hitachi Maintenance, I'm still surprised they aren't building their own depot to maintain the 810s, since they have done with pretty much every other fleet, rather than letting the ToC or another maintainer look after them.
Other uses could include, hold your breath here.
Network Rail.