Building 4+ crucible size ships in a ridiculously short amount of time while also being kept secret is both contrived and bad writing, Bioware needs less contrived plot devices not more of them. As for the council given how Bioware went to great lengths to depict them as idiots its unlikely they're more cleaver than we previously thought, they literally went from believing Shepard at the end of ME1 to "ah yes reapers" in ME2.
You can't ignore trends they give a good example on what to expect and Bioware's tack record with retcon's doesn't inspire much confidence in their implementation.
Again, have a lack of confidence if you want... but what you're tearing apart here is NOT Bioware's retcons... It's the "possible" retcons being thought of by BSNers... and their "opinions" about what is and is not evident in the trailer are as valid as your own. The ONLY time you'll be able to judge the quality of Bioware's retcon of ME:A is after ME:A is released.
Please, show me an image of ARKs being clearly built above earth... can't do it... because Bioware have not released that sort of image. Show me clearly that those completed ARKs orbiting earth could not have just traveled there from having been built somewhere else (and they could have gotten there very quickly since the Mass Relay network would still be intact if it is indeed an image of earth before the Reaper attack). Please also tell me a reason why Shepard would NEED TO KNOW about the ARKs... not that he should be trusted or would have found out about them... but that the Alliance brass would have a reason to tell him on a "need to know" basis. To put it another way - How does knowing about the ARKs help Shepard follow his direct orders?... which are basically to engage in "interdiction" (i.e. basically to STOP the Reaper invasion or at least slow it down)... not to facilitate the "escape" of some peoples to preserve a portion of their species.
I would also contend that building 4+ ARKS in secret in the 3-year period between the end of ME1 and the beginning of ME3 is no more contrived than building 1 crucible in the few months that elapse during ME3... and motivation for making the ARKs Plan A at the end of ME1 could be merely that the tech for them was found in the Refuge System (opened up by Shepard during ME1 by finding the location of the "lost" Mu Relay). No tech for the Crucible was found then (i.e. those plans were found in the Mars Archive after a "desperate" search by Liara). Had the Crucible plans been found earlier, the Crucible might have been Plan A instead of the ARKs.