A decent look at what can be achieved...
http://stadiumdb.com/news/2016/07/new_design_stade_de_france_that_never_was
The stadium was convertable all the time. Very interesting concept
Pretty sure the Millenium stadium can fit a running track and is very multi purpose with lots if different revenue generating events (concerts, football, rugby, speedway, racing, athletics etc) Atmosphere there is very good too