With it looking certainly possible for Celts to get a pick in the first 5, I say it makes most sense to wait for the draft before making a major move. Players available may dictate other moves. If reports on the top players available are accurate, here are the scenarios.
# 1 Pick- They get lucky and take Embiid. With a young center in tow, they could stay pat with there other core players and keep building with draft picks.
#2, 3 or 4 Pick - There seem to be 3 possibilities here. Getting Parker or Wiggins makes Green expendable, maybe to the team that gets Embiid and already has a center (Utah, Milwaukee, Orlando, Sacramento.) Getting Exum could lead to trading Rondo, hopefully for assets that include a big and/or wing scoring.
#5- Smart seems to be best option, which could lead to Rondo trade. Vonleh is also a possibility, which might lead to same plan as with Embiid.
So I say be patient people.