It's almost certain that Ash will lose to Kotetsu - there's simply not enough time to show him battle Virgil. IMO, losing to Kotetsu in a full battle is much better than getting curbstomped by an Eeveelution team in half an episode. On the other hand, this means that all the improvement Ash made in the first 4 leagues goes out of the window. His awful BW team does not deserve a league win either. Ash's battling skills were always better than his current state, even in the Indigo Plateau tournament.
There's no chance that the writers will reduce Ash's full battles into montages because he's the protagonist. The writers clearly want the league to end quickly so that they can concentrate on messing up the Episode N saga.
Maybe Ash will become a league champion in another ten years... or that's me being too optimistic.