I'm not sure it will be a failure, but i do believe that the most important features for BFA are a flop.
Warfronts just seem like an absurd feature. 20 player PvE scenario with an npc army? Sort of like an enhanced Alterac Valley with just one half-sized faction, and npc troops\upgrades? Ugh. They could just feature a couple of raid encounters with said ideas to test it instead of publicizing it as a main feature, since it just seems so lackluster.
Island Expeditions are just... weird. It's like MoP scenarios are back with several paths\variants. It just doesn't seem 'exciting' at all, but i believe they 'can' be fun.
And that's that... the two top features just seem to be uninteresting from the get go.
That being said, as long as end game content is fun with the new raids and dungeons it will be fine. I only hope they expand upon Mythic+ with more affixes, more dungeons (even scaling older expansion ones).
Older expansions hit home runs with stuff like Transmogrify, Mythic+, new classes... in comparison, BFA new features are just average at best. But the 'base features' (new zones, new dungeons, new raids, etc) will be enough to make it fresh and purchase-worthy.