Unlocking All Champs in Custom Game (Suggestion)

I know I may have this in the wrong spot but I am certainly willing to delete and post in the proper location. Just let me know in comments.

Tbh I was wanting to try the new champ Kayn today but sadly I don't have 7800 ip too spend on him. Then a thought came to mind, why is there no way to try a champion before you purchase it? So I decided to make this post in hopes that somebody from Riot would see it. I was thinking why not make it so all champions are available in a custom game, or at least the practice tool. That way if you wanted to see how a champion feels and if you would like him or not, you could go into a custom game vs bots and test out his/hers/its mechanics and abilities. Just a thought I wanted to throw out there.