Blizzard released a few hours ago a more comprehensive web page regarding Patch 2.4's main features; an in-depth look at the lore behind the Sunwell Plateau is also given. Here are links to the highlights:

Sunwell Plateau
Sunwell Isle
New Daily Quests
Global Arena Tournament
UI Improvements

As usual, a trailer comes to foreshadow the release of a new instance:
Sunwell Plateau Trailer (Stream)
Sunwell Plateau Trailer (Download)


Now onto the Season 4 Arena rating requirements as stated by Drysc -- bear in mind that these are preliminary informations:

There will be no changes to gear availability/rating requirement until Season 4 starts, which will not begin when patch 2.4 goes live.
When Season 4 starts here's what will happen:
* Season 1 removed
* Season 2 moved to honor
* Season 3 rating requirements and prices lowered
Shoulders : 1950 rating
Weapons : 1800 rating
* Season 4 gear added
Season 4 isn't expected to begin any time soon, but as always we plan to give at least a two week notice before it does. Stay tuned to these forums or any of your fine local fansites as I'm sure the information will spread fairly rapidly once we do announce a Season 4 start date.

Season 3 prices and Season 4 rating requirements are not yet announced. All information contained herein is of course, as always, subject to change.

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any ideas what happens to my s1 gear do i keep it or is it upgraded

You keep it, that is all.