Point remains though track size is a constant and there is no example of a track being fitted into a tight football stadium, be it one yet to be built or a 100 year old one.
Not saying it cannot be done but it would need movable stands and/or a temporary configuration like the Etihad.
I think there is a slight difference between a new stadium and a 100 year old one. The footprint is tight but advancements in technology will give the architect freedom to review new ideas.
It maybe as simple as removing seats and placing a platform. Comparing to an already built stadium is a bit of a stretch as we are starting from scratch; so certain mechanisms can be incorporated if needed