This may be a bit difficult to implement, but I feel like it would be really cool to be able to drop pokemon that you want trained off at the pokemon tower. When someone who has space in their party to train goes into the tower, day care pokemon get added to their party. There can be a rate per how much xp gets earned, x amount of cash comes out of the owners bank and put into the trainers account. This would be a nice money making system for people who enjoy the tower. Also helps standardize a very common service and make it easy.

+1 I agree but with some changes which are even harder to implement into the game.

A player can select a Pokemon aimed for training and give the pokemon an amount of Pokedollars to hold (Only available in Trainer's Tower and nowhere else). Whoever wants to train a pokemon can choose which pokemon to pick according to the levels he wants that certain pokemon to be trained.
For example : I want my Clefairy to be trained to Level 85 when it's currently level 20. I drop my Clefairy with 135k Pokedollars and whoever wants to train it can easily get it and train it.