At least, not in the sense of purchasing a new expansion. (according to me, a nobody)
There will be no further "expansions" as in purchasable new content. All new content will be included in the monthly fee. This is the reason we saw the dark below trade marked and pulled off. It is blizzard throwing everyone off the scent, or the trademark was filed, and in the time between filing and cancellation, the decision was made not to physically sell an expansion. I do believe dark below will be the "next expansion" but as it is technically a patch, there is no need to trademark it, just as they do not trademark current patches.
Why would blizzard do this?
A few reasons.
1. every time a new expansion comes out, the ability to gain new subscribers drops. A new subscriber must purchase each expansion previous to this, as well as the current expansion. Sure there is the battle chest (vanilla through cata) but any new player would also need to purchase mop, and then the new expansion. This deters many people as there are now so many games that are free to play, or free to play with purchase.
The model blizzard uses most to sustain them is the monthly sub fee for wow. So eliminate the expansion fee, and gain more players over all, and retain players longer. Players are more likely to stay into a new "expansion" if it is included in their monthly fee, or to return to experience content if they do not have to pay for an entire expansion.
2. Speed. If there are no new physical releases of expansions, but rather expansions are released by patch, then it is much easier for blizzard to release content in a faster manner. Imagine patch 1 of the new expasion release 2 new areas, and allows you to level from 90-92, introduces 1-2 five mans along with heroic, and tier one raid. Patch 2 releases an additional area, an additional level (making catch up in raiding much easier). Patch 3 introduces 2 new levels, 1-2 5 mans with heroics, and tier 2 raid, and so on and so forth.
By doing it in this manner blizzard will be able to always have fresh new content every 2-3 months, moving into new Lore expansions annually.
3. Over all cost savings. Sure expansions provide a single one time boost to blizzard, but there are many costs that can be avoided by doing only digital patch releases. Think of how many game copies were produced and must be destroyed because they are no longer viable (original wow, first battle chest, each expansion copy, etc). Not to mention the cost of transportation, copywriting, and legal fees in foreign countries. Yes over all this would mean less "bump profits" but could provide higher profits over all if they can use this to bring in many new players.
4. It would bring back players who left. If you left wow, and you heard that you could rejoin for a new expansion, without having to pay for a new expansion, there's a high chance you would return, at least temporarily from patch to patch for the low cost of the sub fee.
5. Beta launcher is key. Blizzard has recently introduced a beta launcher which allows players to download all trial versions of games, and launch them from one handy program. Undoubtly heroes of the storm and hearthstone will be added to this program. (if you have not downloaded it I highly suggest it). It is forseeable that in the future blizzard will offer a gold subscription, that will offer subscriptions to all games without cost of expansions.
Over all blizzard is a very healthy company. Along with activision they hold titles such as Wow, Diablo, Starcraft, Call of Duty, Skylanders, etc. Their profits have gone no where but up, and wow, even though it has lost subscribers continues to be the largest subscription based game in world history, and shows signs of continuing into the forseeable future.