Fringe theory - what is the Observers’ goal ?

So, we were chatting Fringe theories with spareourworld when a good one came up.

What if the Observers were sent by someone (possibly Peter) to make sure nobody disrupted certain past events ? (think Terminator) That would be why they were seen on numerous times through the centuries, but why they should not interfere. Ever. For fear of damaging the continuity of the time line.

Say Walternate, amongst others, will, in the future, discover or create a way to travel through time, or at least to jump from one event to another. Given he is so focused on destroying the BlueVerse, he could be capable of trying to cause its end by changing some past events, where nobody could track him down. 

What is unclear to me is when would he have taken possession of that technology, and where ? I’m guessing in his universe, in a close future, given they are more technologically advanced than us. But now that Peter has created a bridge between the two universes, both futures will be different (he created another fork in the road, see my previous theory here). But maybe Walternate took that decision in the new future, and because he comes back so far in the past, both universes weren’t divided yet. So Peter was needed to allow the ‘new’ future to be created. Once again, see my theory about the grandfather paradox, where all the universes cannot exist without the others…