We got two cases in DnD history.
3 to 3.5 not compatible.
4Ed then 4ed essential, fully compatible.
For now is a marketing announce.
But I guess it’s really straight forward to rebuild the classes and keep them compatible as the 4ed Essential. Clean up races, feats, spells, monsters, magic items, can be done with 100% compatibility. For resting they can rebuild classes and not using short rest features, they will become pretty much like actual rogue, and be 100% compatible. They won’t touch skills, action, reaction, possibly use less bonus action.
For sure we gonna have a lot of UA and survey on the subject.
3 to 3.5 not compatible.
4Ed then 4ed essential, fully compatible.
For now is a marketing announce.
But I guess it’s really straight forward to rebuild the classes and keep them compatible as the 4ed Essential. Clean up races, feats, spells, monsters, magic items, can be done with 100% compatibility. For resting they can rebuild classes and not using short rest features, they will become pretty much like actual rogue, and be 100% compatible. They won’t touch skills, action, reaction, possibly use less bonus action.
For sure we gonna have a lot of UA and survey on the subject.