ALL Champions Should be Available in Custom Games

There are lots of champions in the League roster at the moment with more to come, and I like that about League, because there is so much variety in gameplay and mechanics. The only problem I have is when there is a champion that I want to play or at least want to try playing. To do so, I either have to buy the champion or wait until they enter the free-to-play rotation. And we all know that is a long wait, because champs would come around averagely every few months. The argument I want to make is that all of the champions should be free-to-play in custom games. We can choose any bots to play with or against so shouldn't we be able to play as any champ as well? Custom games don't give you XP or IP anyways, and it would be good to try out champs in custom games before buying or playing them in PvP games. That way I don't have to use a refund point to give back a champ I didn't end up liking after all, or losing a PvP game because I didn't know how to play a champ mechanically.

These are my thoughts and I would really love to hear what other people have to say about this idea (particularly you, Riot).