UCM Dev Board

I have a UCM Dev Board with a UC5550
I know that UCM550 will not be compatible with TinyCLR 2.0 but can I still use my Dev board with the new upcoming module ?

Mostly yes

What are the major incompatibilities ?

SPI1 bus and other minor pins are incompatible. Power/USB/Ethernet/display and other major features are compatible. You can easily check the G400 datasheet to see what pins are there.