Incorrect. Cata lost millions before MoP launched. MoP regained subscribers during the expansion and did not have a noticeable dropoff in subscribers until the last content patch dropped and the 14 months drought set in. MoP would be the last expansion to not have a substantial dropoff in subscribers before the last content patch dropped. Every expansion afterwards had a huge dropoff after launch and would never recover during the expansion's life cycle. Going by official numbers, WoD was the expansion that lost the most subscribers, losing millions before Hellfire Citadel even launched. If you go by estimates, then Legion lost the most subscribers, losing millions before Antorus even launched.
Correction: the gargantuan marketing push for WoD regained the subscribers... for launch. WoD (and every expansion after it) had little player retention.
Incorrect. WoD had little content because after 5.4 released, Blizzard doubled the size of the WoW dev team. Brook's Law was in full effect here, and the WoW dev team produced less because the newbies weren't really developing much, and the veterans had to spend less time developing content and to instead teach the newbs the tools and bring them into the production pipeline. It wasn't until Legion expansion cycle that the whole dev team was up to speed.thanks to MoP being a failure they had to cut content.
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I don't see how Vulpera would have appealed to the FFXIV crowd. FFXIV players are into anime aesthetics, as in petite girls and lolis and bishounens and such. The only WoW race that vaguely comes close to that are Blood Elves, and they were already in WoW. Vulpera appeal to furries, which WoW had already long appealed to with Worgen and Pandaren (and, if you stretch it, Tauren. But Tauren didn't look very appealing to furries originally. It wasn't until the WoD character model overhaul that Tauren were redesigned to look more furry).
I do agree that wackier races like Centaurs and Qiraji/Nerubians/Mantid or Tolvir or Naga would have been much more welcome than Vulpera.