What if it were something more along the lines of:
90-95, full-sized Draenor continent on opposite side of the sea from the section that forms Outland, where you assist the Draenor natives in various battles and quest-type junk, a bunch of instances within this "past" as well as the raids of the first tier (Shat, or whatever).
95-100 The same continent but in current time, a separate shard of the planet from Outland that has also managed to survive, but the mortal races, etc, were not aware of it, because it doesn't have access to the dark portal or portals back to the Outland section. The legion has not only retained its presence on this "shard" it's built the entire continent into a heavily fortified outpost, and now has moved it back to it's original location, so that it is hovering right next to outland (with crossable points at Netherstorm and Shadowmoon. (KJ is there in command)
So the expansion goes like this:
The legion shows up on this new continent out of nowhere, Netherstorm is immediately lost, but the Ogres and Mok'nathal in Blade's Edge manage to form a solid defense on the border of the two zones, stop the bulk of the advancement. This ties Ogres into the Horde.
On the opposite side of Outland, the legion has attempted to start a similar invasion of Shadowmoon, only to be halted by the combined forces of Ashtongue revival and the redeemed Arrakoa of Skettis. Turalyon and alleria who were stranded on this other "Shard" have joined up with them and the forces of Alleria stronghold, to hold the line at the border between Terokkar and Shadowmoon. Thus tying the Arrakoa into the Alliance.
Outside of these highly contested zones, the Legion is launching renewed offensives via small portal and infernal strike across Outland, resulting in the 60-70 zones being updated to reflect current lore, and Shattrath city being attacked and partially destroyed, made into a minor hub with some underground instances or something. The neutral forces of Shattrath have retreated to Black Temple, which is now the most defensible stronghold on the remnants of Draenor.
In order to initiate the counter-strike against the legion, and to assist in putting an end to the last efforts of the Infinite flight, you go back in time to the old "shard" section of Draenor, deal with stuff there, and plant a number of magical devices that will draw and charge from the arcane energies that end up tearing apart the world, you finish up in the past, return the present and activate the devices, which have been hidden all this time and are of course charged in the present-- This makes some massive permanent shield around Outland to protect it from invasion. And the forces are now free to move across to the current "Shard" which a horrible, dark and twisted version of it's past self, under heavy legion control and filled with foul, fel-tainted wildlife. You do stuff and there are more, completely different dungeons here.
BT acts as a hub between the two times, with a massive permanent portal that sends you to a Bronze outpost in the past version of the "shard" and devices that shoot you across the gap to the current version of the "shard".
Expansion Tier 1 features raids in past "shard", Tier 2 features the final war against the Infinite flight, taking place in the twisting multi-time tunnels of the Caverns of Time (Sori dies), some of the tunnels leading to open pockets of history with dailies and chests and rares and all that other jazz, and then the final tier is KJ's fortress on the "shard".
Rather long winded, but I hope my point was made.
It can be done while not screwing up lore AND progressing the main storyline.
Simple enough to just have a quest early on that gives you a buff that makes you appear to the native people as if you belong there, while not changing your appearance.