I'm becoming more and more convinced of a time loop. the alt timeline, in my opinion is how things played out after MiB has achieved his goal and killed jacob. he doesnt seem bothered at all about the island, insisting that it doesnt need protecting. and in this iteration, he has clearly left the island, and as a result with nobody to protect it, it is underwater
obv this theory doesnt adequately cover certain aspects of the alt timeline, like what is going on with locke's dad, and if the "dad" they were referring to is really anthony cooper, is he a nice guy now? and if so, how is locke in a wheelchair?
i think these, along with other differences are the result of jacob NOT touching the "candidates".
i always HATED the term "losties" referring to the survivors, it sounds a bit gay, i think its better now we can refer to them as "candidates"