Time's POTY won't be Sanders, Clinton, or Trump. It will be ISIS.

[onenote]

4. The results of the readers' poll have never influenced Time's decision

They've been doing the readers poll since 1998 and I don't think the winner of the readers' poll has ever been named the POTY. And with good reason. The results of the readers poll have in many years been downright absurd.

In 1998, the winner was Mike Foley, a professional wrestler. In other years its been Kim Jun Un (the magazine's pick: Barack Obama). Mahmoud Ahmadinejad won the poll once. Last year it was Narendra Modi (the magazine's pick was Ebola Fighters).

How silly is it? Well, the readers poll allows you to vote yes or no. In 2011, Turkey's Recep Tayyip Erdoğan (probably less of a household name than Modi) crushed the competition in the yes vote category. He also crushed the competition in the no vote category.

The standard by which the magazine claims it selects the POTY (although one can debate whether their choices always meet that standard) is the one mentioned in my OP: for good or bad, what person/group/object most influenced events in the past year.
If Sanders wins the nomination next year and wins the presidency, he'll be a shoe-in for 2016 POTY. But this year? It's not even close.