I hope I'm not reviving an old thread/lost cause. I would recommend a double's battle ladder fully; as double's is indeed a entirely different experience as opposed to single's. It would be interesting to see what Pokemon arrive in what tiers. However the basic's have to be initiated, that is the forming the double's half and using good marketing/advertisement strategies to convince people to come towards trying out double's. This way those people who are trying out this new "double's ladder" are essentially "beta testing" how double's will play out. Over the course of a couple months of these "beta testers" the tiers, ban list, universal rules/clauses, ect. shall be established because the community has developed them. This is how I believe the competitive "metagame" for Pokemon was first developed and how a double's metagame would be created.
That paragraph above is what I would make the floor plan is to initiate the doubles ladder. This paragraph deals with why Smogon would want to include an entire doubles ladder in the first place. The concept is quite simple, with a double's metagame there is potential to Double Site Traffic; that is the number of people who use Smogon and Shoddy. the reason behind this is that there are a unsaid number of people who enjoy double battling, however do not enjoy single battling. These people would be using the double's ladder primarily, then eventually wean into singles. They will use Smogon strategies on double's as well as single's for battling, thus now we have single competitive battlers and double competitive battlers visiting the site on a daily basis. This all however is based on good advertisement or "spreading the word" to all single battler's and potential double battlers.
This will especially benefit Smogon if all work done is volunteer work and if Smogon is the first to pioneer this kind of battling.
This brings us to another reason why Smogon would want a double battling ladder, that reason is to be a pioneer in a whole new Pokemon meta, being a pioneer in something means that you potentially have total control over it, an example being how Apple has total control over their Iphone. That and you have the glory of "being first" and being the best.
Having double battles in Smogon will provide one final aspect to the entire Smogon site, this aspect is even further enhancing and diversifying the culture and community that Smogon has created. There will most certainly be many more things to talk about with a double battle's ladder, and it will most definitely help with the singles overused mentality that everyone has. Face it, double battling real people is fun, there are far more factors within the battle, and leaves the battler with an overall better feeling in the end compared to a single's battle (unless your opponent is a jerk).
Now that we have gone over how the double battles ladder will be initiated and why it would benefit Smogon we should go over the core rules that will found double battling.
The game mechanics should be standard double battling in Pokemon correct?
As for Pokemon slots we should not go with only 4 Pokemon as this is apparently unfavorable, not only is it unfavorable but it shall not appeal to potential single battlers who are thinking about trying out double battling.
These are all the rules that I can think of at the moment, we should make sure we got a game plan properly lay'd out before trying anything when it comes to double battling.