When considering candidates for the Great Filter, you must keep in mind that it stopped all the to-be universe conquerors in our past light cone. Your suggestion doesn't seem that insurmountable.
Agreed. I don't think that much of the filtering strength of the great filter is one specific epoch. But within the epoch of civilizations it may be that a large part of the filter power is right now.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.
Notes for future OT posters:
1. Please add the 'open_thread' tag.
2. Check if there is an active Open Thread before posting a new one. (Immediately before; refresh the list-of-threads page before posting.)
3. Open Threads should be posted in Discussion, and not Main.
4. Open Threads should start on Monday, and end on Sunday.