You won't see a 777 ever at STL. Additionally, you will not see any 737 or F-100 at STL in the near future (especially true of the F-100).
If AA introduced those aircraft types, they would have to spend additional money for parts and training just to support these aircraft. In today's cash crisis, there are better things to do with that money. Also, with the F-100 retirement a little ahead of schedule, you won't see them in any new cities, but rather them disappearing from existing cities.
The only routes that AA would potentially fly the 737 out of STL would be on an overwater route as all AA 737 are capable of fulfilling that mission. However, since narrow-body overwater routes out of STL are currently flown with AA 757 rather than former TWA 757, it makes no sense in add in a 737 onto a route unless for routing purposes.