Something that I look forward to is an attempt to balance weathers a bit. Ever since Mollux, I've been trying to get a feel for CAP. Of course, this means creating my own fakemons.
As it stands, there isn't a lot of incentive to run anything other than Water. Too many things reap rewards from it. Some have nothing to fear from the moves boosted by Water. With Sun, everything with chloro is weak to the moves boosted by sun. Solar power limits the life span of everything with it. Sure, dry skin gets rid of the pesky water weakness, but you are taking damage every turn from the sun. Flower Gift is only on Cherrim, which is nuked by even weak Fire moves. The same problem befalls Leaf Guard.
Sand is about the only viable alternative to Rain. I say this because a few pokemon have been placed on the banlist thanks to their Sand boosted abilities.
Yeah, I ignored hail. Not much to say about it. Least supported of the abilities. Fewest pokemon reap any rewards from it. Abomasnow, Mamoswine, and Froslass are the ones that make the most use of it. OU and UU. The rest of NU or LC. And I think only Aboma is OU because of the lower tier bans on weather.
What I am trying to say is that Rain dominates OU and CAP. If you are not running Rain, you are trying to screw with your opponent's Rain. Necturna doesn't fear fire as much. Mollux becomes a huge pain. Argho, Krilo, and Cyclohm all directly benefit from rain. Voodoom deals with all Electric issues.
I guess I am looking forward to one of four things with CAP4. (1) Something that gives rise to Sun; (2) Something that gives rise to Hail; (3) Something that thrives in no weather; or (4) Something that thrives in all weather. Basically, something that brings variety to the metagame beyond Start Rain/Sand, use -mostly- CAPmons.