The idea suddenly struck me today of a new mechanic for quick/fun EV training, and that'd be a sort of pocket dojo feature where you select one of your monsters to instruct other monsters on their form, like a coach or a spotter
The spotter you select would determine the "intensity" of the training, aka the EV yield, via their species
For example, Machop, Machoke, and Machamp give 1-3 Attack EVs, as it is their highest natural stat
Therfore, if you had a Macho family member lead a "class", a generic animation of your pair of selected Pokémon tweening weights up and down or using a punching bag would play, and either you'd set a timer for your Pokémon to train a specific amount, or you'd do it manually with timed taps of the A button until you have the points you desire
In addition, if the Pokémon you have acting as a coach has a nature that corresponds to the stat youre focusing on, it could increase the effectiveness of said training
If both the coach and student have natures corresponding to said training, it would increase effectiveness even further, as they get a good rapport going
Conversely, if you have a Machoke that was Timid, you could use him as a negative trainer, and he could give your Pokémon sloppy or clumsy training that would reduce your attack EVs, as his heart just isnt in the training

So far, I think
HP - Eating Contest/Bulking
Attack - Punching Bag
Defense - Sparring/Blocking a Pitching Machine
Sp Attack - Target Practice
Sp Defense - Waterfall Training (Mind over matter)
Speed - Treadmill
Sauna - No coach, just a hard EV reset