There's a surprising amount of flexibility with PanelView Plus and FactoryTalk View Studio.
If you have FactoryTalk View Studio ME version 6.10, you can create *.MER runtime files for any PanelView Plus terminal with version 6.10 or earlier firmware, all the way back to version 3.20, which came out 11 or 12 years ago.
And in general a PV+ can run an application built for any previous version; a PV+ with version 6.10 firmware could run a 6.0 or a 5.10 or a 4.0 application.
The two big pebbles in the pudding are ActiveX controls and KepServer drivers; you can't easily mix pre-v6 and post-v6 versions.
Ideally, figure out which revision your PV+ terminals are and when you create a Runtime file, create it for the same revision.
Remember that there are two modern operator interface terminals that share the PanelView name but don't run FactoryTalk View ME; the PanelView Component and the PanelView 800.
I'm omitting discussion of the PanelView Plus 7, which is a new hardware platform that runs limited-scale FactoryTalk View ME applications; I don't know if they'll run a Runtime built for version 6.10. Tradition says they should, but I haven't used one yet.
I'm also omitting discussion of the PanelView 5000 product, which is all-new and not yet released.
I'm attending a "Rockwell Automation On The Move" event next week that will have some of those new platforms for discussion and examination and look forward to seeing if they're enough to lure me back to using PV+.