I'm the biggest playable-Vrykul advocate there is. However, the more I look at models and the more I think about it, the more I'm convinced the Alliance will get Kul Tiras human models as an Allied Race. BUT, if Blizzard plays their cards right, it might be a choice Vrykul fans can get on board with.
Theory: Kul Tiras player characters are Half-Vrykuls
Because I speculate that neither Vrykul or "fat humans" would be an accepted idea by the community to substitute for Humans, I am presenting the suggestion that instead, the inhabitants of Kul Tiras are actually between Vrykul and Human in the evolutionary chain. A "Half-Vrykul", if you will; like a Half-Giant in standard RPGs. I'll be covering the following four lore based areas to support this theory: History, Geography, Place Names and Culture. Then I'll conclude with screen shots of the large Kul Tiras male.
History:
Throughout WoW we have been given the history of the Vrykul and Humanity. In a nutshell, the Titans/Keepers create Iron Vrykul, the Curse of Flesh makes them Vrykul, and the curse evolves to cause them to produce smaller offspring. At some point Vrykuls migrate to the Broken Isles in Stormheim, and another group flees with the Keeper Tyr to what becomes Tirisfal. The smaller offspring eventually become what we know as Humans.
From Blizzcon we learn Kul Tiras is an "Ancient Human Kingdom".
Geography:
Here is an image of Kul Tiras from Blizzcon. It is placed directly between the known Vrykul locations of Stormheim and Tirisfal, and south of the Howling Fjord in Northrend. Ancient Vrykul must have set foot on the islands of Kul Tiras at some point in history.
Place Names:
In Northrend and the Broken Isles we have Vrykul settlements with nordic sounding names like Valgarde and Nifflevar. The Vrykul that accompanied Tyr at his death site named the area "Tyr's Fall" which later became known as Tirisfal.
In Kul Tiras we have towns named Tiragarde Sound and Drustvar. Is it too much to conject that 'Kul Tiras' might also have once been named for Tyr?
Culture:
Both Vrykul and Kul Tirasians are nautical cultures. Ships and sailing are not just part of their lives but the focus of it. Both take pride in monster hunting. Both have fringes that worship death magic.
Examples:
Here are some screenshots of Kul Tiras males in-game. Some to show the physical relation to Vrykul, and others to show the size differences between Kul Tirasians and Humans:
Standing Kul Tirasians vs standing Human female
Sitting Kul Tirasian vs standing Human male
Vrykul looking Kul Tirasian
Finally, here is a composite of the stock Kul Tiras male with a Vrykul beard. If this isn't enough to excite you as a Half-Vrykul allied race, I don't know what will.
Conclusion:
Based on the shared History, Geography, Place Names and Culture of both Vrykul and Kul Tiras, it is clear to see the influence of the former on the latter. Coupled with the obvious size differences between a Kul Tiras male and a typical Human, and it's hard not to argue that these men are more closely related to Vrykul than the current playable humans (without the "getting-through-door" problems!).
With some minor cosmetic tweaks, a Kul Tiras Allied Race could be added to the Alliance as an effective playable Half-Vrykul.