Before I begin there is a possibility that I am just repeating what has been said before but since I have not seen this theory either here or the BioWare forums it could just be paranoia, either way I apologize if this is a repetition of thoughts.
My major concern with the ending(s) of ME3 is that regardless of all the plot holes and potentially ret-con material, the current canon ends in one of two ways, one obvious, more or less based upon given ME information, (regardless of before mentioned plot holes) and one that most people may forget. Both of these endings ultimately restart the Cycle in their own way, and both are just as bleak.
First, with a new society of people presumably descendants of the Normandy crew^1, yet somehow human, (or at least appear human) that have legend of "The Shepard"^2 that has allegedly been passed down throughout the years.
Taking into account the fact that this would likely be an oral tradition (as the only technology would be the Normandy, which won't last forever) many things would likely be altered (as the Stargazer pointed out). However, as in many current and historic oral traditions and stories go, while the details may be lost key ideas will always be consistent. These ideas would be that "The Shepard" defeated the Reapers by sacrificing himself, the Citadel and the Mass Relays to save us all from extinction.
Since the child asked if he would go to the stars too, logically he would ask what the Reapers, the Citadel and the Mass Relays all would be and, even after withstanding the test of time those answers would basically boil down to being correct^3,4,5. The boy also asked if he (the future of his society) will ever be able to see the stars, to which the Stargazer replies "When you are old enough" (or something to that extent).
Here is where ME3 logic issues arise. God's Child tells Shepard that organics will inevitably create synthetics and that these synthetics will ultimately destroy their creators^6 it may also be inevitable that, given the stories passed down throughout this culture, they will try to rebuild the technology of their god/gods/elders and ultimately concluding with a Promethean result of creating their demons as well. Sovereign even explained that with the Mass Relays, or in this case with the knowledge of their legend, Society is blinded to use them instead of coming up with an alternative.
The second, and perhaps more interesting idea is that after the ending of ME3, there is at least one surviving sentient species in the galaxy, the Yahg. Hackett explains that the Reapers had not invaded Parnack, assuming because the Yahg were pre-spaceflight, this means that possibly in only a few short centuries they would develop spaceflight.
After the destruction of the Relays, and the potential destruction of all the Reapers, the Yahg would have all the time in the world to explore the galaxy^7, and in a short time (on a galactic scale) they may even discover a Reaper corpse or the debris of a Mass Relay. Either of these discoveries would be alien, literally but no pun intended^8, to the Yahg, as the only members of their species to know of the Galactic Community is the now deceased Shadow Broker and the other kidnapped (but then killed) Yahg, the kidnapped subjects on Sur'Kesh^9, and the Yahg who were immediately involved in the Council Representatives massacre 60 years prior^10, and none of these people would be aware of the Reapers or the Relays anyway.
The Yahg would then, eventually, discover a Reaper corpse and slowly be indoctrinated by said corpse until they were ultimately told how to build the Relays, then likely reawaken or rebuild the Reapers. This is similar to how the Reapers used the Keepers and the Collectors as tools to do their work.
While both of these ideas may sound farfetched neither are outside the realms of possibility (especially after the M. Night Shyamalan ME3 ending). Both endings would also ultimately restart the Cycle, and may in fact be part of a larger Cycle that includes the Reaper destruction/recreation in its progression.
While this, in a way, may sound like an Inception type twist to an already convoluted tale, it actually may actually make sense with information already established within the Mass Effect Universe. The Prothean VI on Thessia says that each Cycle before all had distinctive cycles within them, for example needing the Krogan to stop the Rachni then needing the Genophage to stop the Krogan, and each Cycle all had these distinctive inner cycles, Javik also confirms this by saying that during his Cycle that there were many smaller wars before the inevitable Reaper invasion. With these facts in mind it is not outrageous to believe that the 50,000 year Cycle are all just part of a larger Cycle.
This is why I believe that the ME3 ending is so dark, it will ultimately, according to God's Child, result in the Cycle repeating itself and this is my main concern with this ending being the final, and true ending, if what we have now is indeed truly that.
This, again is all just my speculation, feel free to comment, criticize or add in any way you like (just do it neatly please). Again I apologize if this is an already stated opinion or idea of an eventual conclusion and if that is the case, if you can site it I will gladly relinquish all claim to this idea (unless I did it neater, I'm kinda proud of this layout) and give my full support to whomever thought of this first, and thank you for your time.
FOOTNOTES
1) This is my belief as the scene with the Stargazer and his grandson have the same moons and night sky as the planet the Normandy crashed upon.
2) Just bare with me and go with it for now; it makes me cringe to say it too but just place yourself in this society and it would seem right.
3) Space Monsters bent on destruction of all those that are not themselves.
4) The Space City where all people met and where the elders resolved their issues.
5) The machines the elders used to fly across space to meet one another.
6) Despite the fact that this is disproved with EDI, Legion, and the Geth, but again bare with me.
7) For the sake of this theory assume that Parnack is not in a system with a Mass Relay.
8) Maybe a little.
9) Who would have been stuck there when the Relay exploded, as I doubt they could learn a new language in a matter of days then and how to operate a space ship that is built in that language.
10) To me this would have resulted in either a Roswell, Parnack situation that would be covered up by their government or an alien abduction story that, on Earth at least, no one actually believes.
11) They were after all said to have intelligence of the Salarian.
EDIT For the sake of the second argument also assume the Elcor were eiped out militarily above Earth and were already on the verge of destruction culturally by the Reapers on their homeworld. I seemed to have forgotten that they do not have a Relay in their system but again it is not much of a streach to say they died out based on codex entries on their colonization strategy, or lack therof, and the fact they were densly populated on their home planet.