Many players want to buy new champions to increase their champion pool. However they feel hesitant to do so because IPs are hard to grind and also because they don't know if they will actually like to play the champion. Right now, if they buy a champion and then realize they don't like to play it, they are basically throwing out a lot of IPs. To prevent this problem from happening, my suggestion is to add a weekly free champion of the players' choice to the weekly free champion rotation. By doing that, even if the champion they are interested in is not in the weekly free champion rotation, they are able to chose and test the champion before buying it. However, to prevent some "exploits" there are a few rules.
1- The chosen champion is only unlocked for 1 or 2 days instead of 1 week.
2- The chosen champion is only be available for normal/bot games.
3- The players may chose one champion every week but each champion can only be chosen once every month.
Share your thoughts in the comments below and leave an upvote if you like the idea.
EDIT: There are many other ways to implement this idea. Either way, all that matters is that players can test champions before buying them.