Thanks for the detailed post! Personally I always prefer to take the conservative approach with IRS. After reading your post I'll treat ICOs and exchanges between virtual currencies as a tax event. Hopefully we will get clearer guidance soon.
BTW, this brings up the question of whether choosing the conservative approach here is indeed elective, i.e., should IRS provide guidelines in the future that the aforementioned events do qualify for 1031, would you then need to amend your return even if you prefer not to?