we could save a lot on fuel if they reordered flight plans into a grid, you might not be going direct to somewhere far and popular but they overall impact or the environment would be huge.
What do you mean by a grid? Long-haul direct flights offer many benefits, such as lower drag at cruising altitude, engine efficiency at altitude, etc. [1] Biggest fuel savings are going to come from more efficient engines and weight reduction (composites).
1: https://en.wikipedia.org/wiki/Fuel_economy_in_aircraft