Is there any room for a fly over/under either east or west facing from the south sub to the Fife lines at Haymarket junction?
This is getting dangerously silly now...
If you want this for freight, there's no point. There's a speed/weight limit over both the Forth and Tay bridges, so freight gets sent around via Stirling.*
If you want to build this new flyover for your hypothetical new passenger service via the sub, good luck ever getting those sums to work out. It would be silly to invest probably upward of £100m for new infrastructure to allow a new service to run, and a speculative new service at that.
There isn't any provable demand for this new service, and nor will there be until you build three new stations. That's a lot of money spent on guessing there might be demand for an orbital Edinburgh railway.
There isn't even any space along the sub, or at Gorgie, for three or four new, accessible, compliant stations.
*Actually, most freight gets sent via Slateford, Shotts, Holytown, Coatbridge, Cumbernauld and
then via Stirling, but that's inconsequential.