It would appear to me that FTM has 3 choices:
1) Add Date Field to FTM citation
2) Delete Date Field from Ancestry.com (ugh)
3) Map data in Date field in ancestry to export to FTM Citation detail box.
I would think No 1 would be less disruptive to users.
I would think No 2 would be unacceptable to users.
No 3 is just a work-around because the two structures are different.
I don't know how this deals with gedcom compatibility, but the repurcussions of a change on gedcom would need to be evaluated as well.