I think it will boil down to what is the cheapest method to cross the taxiway with the station located in a reasonable distance from the terminal.
The route shown, which actually might not even be the route, would be costly to construct and would cause disruption to quite a big area of the CTA. If the route was accurate it would have to be very high level to pass over the passenger bridge with a high level station equally high and if it went under underground it would have to be quite deep and would have to be bored out at great expense.
There is certainly enough space around Alpha for another cut and cover tunnel if it hugged the existing tunnel on the easyjet hangar side as the taxiway could be diverted as it was back in I think 1998. If anyone looks at a google view of the tunnel the narrow remains of the last taxiway diversion can still be seen as the tunnel was built in two halves. It could then follow the road and terminate somewhere around the easyjet hangar so leaving most of the CTA alone.
It is clear that there is no obvious route either above or below ground or even for a station location so it will be a clever challenge for the team working on the plans.