What do you recommend as an upgrade to the 6100? Are the configuration files from the 6100 usable for new Grandstream PBX systems?
You can move to 62xx series. Configuration is movable after 1.0.13.xx firmware (you need have at least this firmware in current UCM).
If your current requirement are higher you can buy stronger UCM series.
How long will the 6200 series be supported for new features? the 6100 is no longer updated for new features in the firmware
That is a good question, but is unlikely to get an answer. I don’t believe they would EoL the 62xx until they had a newer model to replace it which currently doesn’t exist.
That said it should realistically be a couple years at the least.
any 61xx model can be restored to a 62xx model if the firmwares match(post 1.0.13.x) and any extras are removed if the newer model is smaller.
That means if you go from 6108 to 6204 you need to remove any config for FXO ports 5,6,7,and 8 for the restore to work.