I think this is a very important point for a completely different reason.
The Hearthstone TM does not list mobile devices, and really doesn't make sense for a physical release with a different name.
World of Warcraft already has mobile functions (AH) but it's TM does not have mobile platforms either. So it's unlikely that a TM for a new expansion would list mobile platforms for something like pet battles. Meaning the TM is probably not wow unless they're planning on releasing some sort of tablet format for the game. (Also I mean... it is sort of an unusual title for an addon to an existing game)
We know it's very unlikely that the Heroes of the Storm TM is for Starcraft or Diablo, since the expansions for both are already known.
Which leaves us with two possibilities.
The first is Blizzard All-stars rebranding, which seems to be the proverbial basket everyone is putting their eggs into.
But I feel there are some problems with this line of logic. First, it's a poor marketing choice for Blizzard to sever their link with the first Dota (the All-stars part of Blizzard All stars) and the company recognition that comes from their name being in the title. Heroes of the Storm also partially resets hype and advertising, if you ask a MOBA fan who is not affiliated Blizzard games, if they've heard of "Heroes of the storm", chances are they aren't going to know what you're talking about... if you ask if they've heard of "Blizzard all-stars" chances are much better they'll know what is going on.
Second, MOBAs are just not a game that can be ported to mobile while retaining their competitive fashion. This means that if Heroes were All-stars, the mobile functionality would be side applications like match streaming, leaderboards, etc. Which, let me remind you, is very similar to Wow's current mobile function... something which is NOT listed on the trademark.
I therefore think that All-stars is not as likely a use of the TM as people make it out to be.
But this leaves us with the second aforementioned possibility.
And I'd like you to temporarily suspend your notions about this and hear me out.
There is a note-worthy possibility that Heroes of the Storm is Titan, and here is why.
(NOTE: I am not in any way saying Heroes IS Titan, or even that it is MORE likely than any other possibility, just that the possibility exists and should not be arbitrarily brushed away)
To start with the flimsiest of evidence, let us remember that Titan is simply the code name for the project.
That is, Titan is a project that as far as we know, doesn't have a name yet. An unnamed brand new game. It's my personal opinion that "Heroes of the Storm" is a much more fitting title for a stand alone game than an expansion or addon. It's just that sort of title, unlike, say... Mists of Pandaria.
Titan as a code name doesn't refer to the Titans in wow, but to the general word Titan.
We can assume that Titan is related in a subtle way to whatever the game is about, similar to how Hydra was related to Diablo 3, in that way that Hydras are monsters who are very often depicted with three heads.
The Titans of mythology are primal deities embodying the natural world, and so have a potential connection to the idea of Storms, as well as originating from the same Mythology as the Heroic age (i.e. the age of Heroes). But again, flimsiest evidence.
Many people seem to be ignoring the possibility of Titan info at Blizzcon because of the project reset, but (as I've pointed out in several posts in different threads now) the project was only pushed back to ~2016 release, even if we assume that's a full year off (2017) that's just over three years away. Diablo 3 was announced and fully revealed FOUR years (3 years 10 months I guess) before the game's release date. This means that it is entirely possible for the 2013 Blizzcon to contain the Titan Announcement. The company has been through some relatively hard times recently with the stock issues, Diablo 3 release and WoW's sub decline... A Blizzcon with extensive info on D3 updates and expansion, a new out of the park wow expansion, Hearthstone... a game which seems to have the potential to be quite massive in its own right, AND the unveiling of Project Titan would do absolute wonders to reassure stockholders and force the gaming community to take a second look at Blizzard as the community is being enticed by the next generation of consoles.
The last issue I want to cover is the same one I started with.
The mobile platform section of the trademark. The red flag that is stirring up all speculation about Heroes of the Storm, as it's the only thing differentiating it from previous game TMs. I've already pointed out ways in which it seems odd for the mobile section to be in the TM for Blizzard's current IPs.
But let us consider how it works with Titan.
Unlike the other games Blizzard has, we know nothing about it's gameplay, setting, etc, etc.
One of the few things we know about the game is that it's been planned as a more casual MMO. I believe this is the important point. The mobile and tablet platform is a HIGHLY CASUAL market. The very nature of mobile/tablet devices makes them very suited for quick casual gameplay and NOT suited for any sort of competitive or in depth game.
This seems to me to be a perfect pairing. A new age MMO where significant portions of the game can be accessed through mobile devices and tablets, so much so that it is intrinsically designed to have people using those platforms and actually warrants putting them in the list of Trademarked formats. It's also something that, if done well, could set Titan apart from an MMO market filled with dozens of failed attempts to bring something truly new and unique to the genre--Something Blizzard would clearly have to do if they plan on running both MMOs simultaneously without negative inner competition.
Just my $0.08, apologies if this was somewhat long winded.
tl;dr
-Diablo 3 was announced 4 years before release, meaning we could see Titan at Blizzcon for a 2016/2017 release.
-Titan is a casual MMO, mobile/tablet is a casual platform and separate market from WoW.
-There seem to be large holes in Heroes of the Storm being used for the current Blizzard games.
Heroes of the Storm could be project Titan.