My opinion is that “ladders” won’t be like how they were in Diablo II. That system was meant to address issues with the economy (due to dupe exploits with Battle.net that weren’t 100% resolved).
Diablo III’s technical design does not allow for that same sort of system to work (where your ladder character, becomes a non-ladder one after a reset occurs). One of these is we have limited character slots which are shared between the games two current modes; normal (softcore) and hardcore. A new ladder (aka seasonal) server and associated characters, will share those same slots.
Patch 2.0 with the new account wide Paragon system, addresses this. Basically at level cap on a seasonal character (normal/hardcore), any Paragon experience earned, will eventually shift to ones respective account wide Paragon. The same goes for items (inventory space is going to be the biggest issue when those items get moved from the seasonal characters stash, to its respective normal/hardcore one).
I also believe this new mode (ladders/seasons) will be combined with challenge modes; basically the Nephalem Trials system. Rankings will be based on these challenges. The easiest way to invision what I believe will happen is to look at the current Achievements system. You earn points and also unlock stuff like banners for completing certain objectives. Some Player vs Monster/Environment style of challenge events from Trials (Cursed Shrines and Chests) were included in patch 2.0 which gives a preview of those types of events which goes towards one seasonal rankings. The competitive aspect comes from the actual tracking system which brings the Player vs Monster/Environment vs Player system into play (the dev team has made it obvious that a direct Player vs Player type of arena with an actual scoring system, is not the way they want to go). Instead of achievement points, you would earn points that goes towards your ranking on that ladder. And anything that can be achieved in-game, can be used in this system (who can level to 60/70 the fastest, by class, to Paragon 100, the highest Paragon level in a season, amount of gold collected, amount of monsters killed, amount of elites killed, etc).
The incentive to playing on a ladder/seasonal character, should be in the cosmetic type of rewards in terms of unlocking some in-game/profile visual. The best way is to look at how StarCraft 2’s ladder/ranking system works in that regards where you have individual granular style achievements as well as broader ones encompassing leagues. The biggest difference with Diablo III is that there won’t be any direct Player vs Player type of qualifications when it comes to placement in a league. What I’m getting at is that your points will give you a similar type of “badge” both in-game and on ones online profile for that season. Thus unlike Diablo II’s ladder system, which offered unique in-game item rewards, there would be no such need for that kind of incentive. For those competitive types who want to see themselves in say the top 10, they’ll have that option on the macro leaderboard. Those who aren’t in it for that aspect, can still unlock some nice visual/cosmetic rewards no different than currently unlocking a new banner pattern/sigil.
Since all of this is tied directly into Battle.net 2.0, this also offers the possibility of finally getting forum avatars that are tied to these achievements (as well as bringing achievements that can only currently be viewed via the game client, online to the web profile like with WoW and SC2 profiles).
As to when the D3 developers will have ladders/seasons available, I highly doubt it will be available with the launch of Reaper of Souls. The bigger question though is how much depth it will actually have. Too many systems have been hyped before, where the final implementation ended up lacking in many ways (just look at loot 2.0 for example – extremely underwhelming from what was hyped). Thus all of this teasing, isn’t getting me hyped with the impending launch of the expansion.
