Virgin Atlantic trialled this at Heathrow in 2006[0]. It looks like it didn't gain traction because the airport would need to be resigned to support it, and the landing gear might have been damaged by so much towing.
At least in Europe, except for the largest airports, the start slots are well organized enough that the taxi+wait time is just enough to warm up the engines, eliminating the saving.
[0] https://simpleflying.com/throwback-virgin-atlantics-fuel-sav...