Fixing the budget may get nasty, since the EU countries may have to increase the contributions or slash the expenses or EU bureaucrats may have to accept a decrease in wages. Net contributors like Germany or France will not want to contribute more, since they have their own problems to solve internally and the nationalist parties are on the rise there (Marie Le Pen and Alternative fur Deutschland). If the budget is decreased it will further alienate the East and South European countries. And euro bureaucrats will not simply accept smaller wages.
Also after Brexit the average EU income will decrease so some regions may no longer qualify for subsidies. Slow economic growth, European banks problems, a migration crisis, Germany's wealth dependency on export that is expected to falter, a conflict with Russia, all this won't help in finding a new, acceptable budget.
In the current situation the EU is ready to embrace any solutions that will increase the budget without causing too much friction within the bloc. FTT seems to meet this goal.