I posted this yesterday but i'll post it here since it's the topic of discussion.
Personally i think Movie 16 seems more fitting to take place during Episode N. I'd like to think of the Team Plasma/Genesect hidden plots all grouped together, instead of hinted and then brought back later in an arc that is much less relevant. Movie 1's cameo scenes all took place around the correct time as Movie 1 (even though the episodes were delayed that wasn't the writers fault) so i'd like Movie 16 to do the same.
I never did believe Charizard would stay long, and the length of BWN8 - BWN14 is an appropriate length for his return. If Oshawott does departure (not saying he will) it only supports the fact that Movie 16 does indeed take place before DA.