Creating a new metagame is a waste of time, most 'gimmick' tiers such as cap, little cup and NU barely have enough activity with their small (albeit devoted) community's. Making more of these would just split the limited ammount of people considering to play a metagame out of standard. Effectivly ruining all of them to inactivity
Besides Gen 5 is comming up in a month, as such even if you manage to create a banlist for this. By the time you are finished gen 5 will have started and you might start as well all over again.
edit: it would be nice if they made a rule of this, i've seen a lot of similar topics with 'new' metagame suggestions getting deleted lately
As a CAP player as well, I'm going to try my best to avoid going sour, but ignoring the fact that your post doesn't contribute at all, it's far from a waste of time. First off, CAP and NU are far from gimmicks. If you actually paid attention then you would see CAP has a useful effect on how we look at the metagame, and how it might be reflected in future generations. As for LC and MC, they're also different as they encourage players into thinking with different mindsets than they would in OU or any other standard tier. The numbers are different, the entire game is different, and quite a few people actually enjoy it, since they might like how the particular metagame works. The user base may be small, but that's exactly why there are discussion threads like this, so the people who know what they're talking about can discuss such things in peace and anybody new and interested can pick up on how to play as well.
It's not even that new. It's been talked about and played around with before, and while I can concede that putting the idea into structured motion may be late, it's not like Gen V is going to render everything completely ineffective. Even after the new mons and mechanics, we will still have an idea of what can work and what can't, we will have ideas of what to test and a stable base to test those things off. And even then, think about how long it will take for Gen Vs simulator to stabilze. The user base may be small but like I said, it can expand. Cynics like you just shoot down everything because you're not used to unofficial tiers where things are different and don't follow the metagame trends of standard. This isn't a random suggestion, it's a metagame that's still trying to shape up if you'd give it a chance.
Anyway to get this thread back on track, regarding Chansey - I think, NixHex, because Chansey is almost equally powerful to Blissey and most of the attackers are a lot weaker, that's what makes Chansey so broken - even with things like Rhydon and Lairon, Chansey just provides too much of an immediate stop for specially based offensive teams. Mangeton's only real option is to Explode, while Kadabra has a Focus Bl(ass)t that doesn't 2HKO or a somewhat shaky Trick (if Magneton or Haunter come in).
Offensively, I think the Rock Polish sweepers will be quite decent, since their great coverage and high power will make them threats to deal with. However, as I have found out playing with Pupitar and Lairon, they will find it very hard to actually set up, since their bulk isn't on par with their evolutions, and their neutrality to many common attacking types means they're going to take a lot of damage unless they can force things out. However, DD Dragonair and Scarf Gabite remain the top sweepers, since they both have somewhat reliable options to take out Lairon and Magneton.
Specs Kadabra does hit extremely hard, however, and like I said, if you can get past Chansey, it will sweep teams due to lack of good Psychic resist outside of Metang. Porygon2 is underwhelming, and Haunter needs SubSplit to not be overshadowed by Kadabra, which it still has problems with due to being frail. Scarf Maganeton packs a lot of power, however, so it's not just a steel killer but with a strong, STAB Flash Cannon (which hits a large proportion of the tier for neutral), as well as Thunderbolt, it's my personal favourite for Special Attacking, since if you can get it in on the other player's Mangeton Flash Cannon or Thunderbolt, a swift OHKO with HP Ground before sweeping later or letting Gabite clean up can be all you need.
It is an extremely offensively oriented Metagame, with a race to who can set up and remove threats first. Of course, stall and defensive is entirely possible, as I found out, it just needs to be played extremely well.