treysea,
Are you still looking for help with this?
It is possible to construct a field group based on the selections made on another post. One would need to look at the code that is exported from a field group and how the individual fields are constructed. You can get the other post during the ‘init’ action and construct the new field group.
The hard and important part of what you are looking for is that the field names are the same and the the field keys are both unique and do not change each time the field group is constructed. I think that having a field group that changes constantly would be extremely hard to achieve in a way that would not loose data or cause other issues.
