I still don't see why it even crosses anyone's mind that the reserves being used in the League means the Sinnoh team will be shafted. It won't happen. Each reserve from the opening will probably only be used for a single battle. The Johto starters have a chance of being used like twice, but I doubt it. I expect the League to be the AG Battle Frontier all over again. This time with the battles close together.
Ash used the following the Battle Frontier:
Charizard
Squirtle
Bulbasaur
Donphan/Torkoal (which ever one you consider a "reserve")
Snorlax
Tauros
Heracross
*Vampire-like voice* Seven, seven reserves. Ah-ah-Ah
Ash is using the following in the League:
Snorlax(The writers sure love this fatass)
Muk
Bayleef
Quilava
Totodile
Noctowl
Donphan
Glalie
Corphish
Torkoal
*Vampire-like voice* Ten, ten reserves. Ah-ah-Ah
The AG team certainty wasn't neglected in the BF just because the addition of a few reserves. I'm sure Ash will battle at least seven opponents in the League. About three or four in the earlier rounds and about three or four in the full battle rounds. The Sinnoh team will probably be even less neglected than the AG team when we take into consideration that a good deal of the League battles, probably about half, will be full battles (6 on 6.) Ash vs Brandon had the most pokemon used of any Battle Frontier battle, with both trainers using four pokemon. All of the others were either 1 on 1, 2 on 2, 3 on 3, or double battles.
Seriously, don't expect the likes of Snorlax, Corphish, Muk, and Donphan to get three or more battles. They'll probably get a battle each and that'll be all they wrote.