I was playing the battle tutorial today, and i wished we could use more than just Ashe Garen and Ryze, so i had an idea, what if battle tutorial aloowed you to use any champion you bought as a way to get acclimated and more experienced with it? It would make matches more challenging as well as more fun because people who were using recently bought champions could use them better.

Once you have been through Battle Training once or twice, you shouldn't need the announcer telling you "You've stepped into some brush! Defeat the wolves in the jungle! Use the recall spell to return to base!"

You can create a custom game and fill it with bots on both sides, if you want. That's the preferred way of testing out a brand new champion.

I believe he wants a means of 'testing' any champion he chose before purchasing them.

Here's the issue, testing a champion in battle training doesn't actually give you a good feel for how that champion handles. Heck, even coop or your first few pvp games don't really give you a good feel for them. Beyond that, having 100+ champions to try to choose from is actually rather intimidating for most players. Try playing DotA and having any idea what's going on in your first 100 games, when people aren't mostly using the free week champions. (Here's a hint, you might know what's going on in 5-10 of those games.)