This is it guys, the UBER ultimate new series premise.
An excelsior class Federation ship (circa 2292) is on a routine mission when it is struck by a Temporal singularity and thrown back in time by over 200,000 years to the time of the Iconians and other civilisations long since gone by the time of the Federation. The crew must try to survive in a now unknown universe and try to find a way back to the future, there attempts to remain obscure prove to be ineffective and they get caught up in the galactic affairs of that time period and even end up fighting in a war against an enemy so strange and yet so powerful that the fate of the future may lay in their hands.
Considering the vast difference in technology, any lengthy survival of the Federation ship, especially if the Iconians were really gunning for them, would be unlikely.
Which is what makes it interesting. We've never really seen the Feddies dealing with being totally outclassed in a fight over a long period of time (except for the Borg, which just goes to prove, the writers need to play fair and not give the Feddies a helping hand via arbitrary ass-saves).
Also: no fussing over "restoring the timeline." In the case of the Iconians, nobody really knows enough to say for sure how history is supposed to go, so that allows the boring, tired timelne-restoration angle to be thrown out the airlock from the start.
No it makes it completely unbelievable in the "we're a super advanced galactic empire and even our children's pea shooters could take you out in one shot" kind of way.