On a limited basis, in low traffic, mostly at night, direct routes have been given by ATC all over Europe since it was technically possible to fly them with INS in the seventies.
With a few local exceptions, ATC software has not been adapted to accommodate more direct routes on a larger scale. Technically, there should be no serious problem to let aircraft fly from TMA-exit to TMA-entry. The ATC computers can calculate the significant points and eta's along any random route to a fix. Operationally it would require adaptation of ATC area control working habits including reliance on computer assisted conflict detection (by the planner controller, the executive controller should use but not rely).
The main stumbling block is political, see the uncompromising reaction of Adanakebab. It used to be the Russian threat (and in Eastern Europe I'm sure it was called the NATO threat leading to the same inflexibility), today it is the training for Afghanistan, there will always be some argument to cut off large chunks of airspace from civil use.
More flexible use of airspace brings some relief but that should only be the beginning of opening up more airspace when there is an economic and environmental demand for it.
Keep the pressure on, 6000PIC, you are absolutely right, it's an economic and environmental waste to circumnavigate unnecessarily.