Champions League money is worth a hefty amount to some, clubs will be keen to find a way to see that out. Reducing the amount of games by limiting them to a single leg, nullifying any advantage by having them hosted neutrally is fairly agreeable.
Europa League sticking point is basically the winner gets a CL spot, which is fairly important for the PL teams competing in it. Otherwise the money involved is fairly drab to most teams and cancellation of the whole tournament would be possible.
Also award the FA cup to the top scoring team.