Key points dog. BHD has physical/geographical/environmental restrictions which cannot be overcome.
However within these limitations scope for further evolution exists with the next generation a/c - B737/A320 NEO and coming up on the outside Bombardier C series.
The C series potential is enormous but it is too early to speculate on new destinations at this stage.
Regarding airport closure this is Friday night pub stuff. Both airports are profitable and if the sale of Cardiff to the Welsh government proceeds this could result in significant investment at BFS.
Finally a rail link to BFS is pure fantasy. If it was an economic runner BFS would have found the money already. The taxpayer cannot pay for it! If Dublin cannot make it work.....
BFS management raise this issue periodically to deflect attention from their more pressing problems.