We started a 5e Age of Worms campaign back in April. We converted our characters as much as we could when the Basic rules came out. Anything that was not in the Basic rules, they could keep from the playtest, and we made some changes to the playtest stuff (non-human races got +2/+1 ability bonuses half-orc got +2/+2, backgrounds were limited to 4 proficiencies/languages plus the special feature, spell progressi). When the PHB comes out, we will dump most of the playtest except for the monk who I think might only be in the DMG. This has worked out very well for us, and aside from the little surprises ("charge is gone", "no more sound burst", "fireball does how much damage") there has been no negative impact from the change.
I will say that I am greatly looking forward to monsters being added to Basic on August 8 and the monster manual in September. Converting all of these 3/3.5 monsters or reskinning playtest (and now starter set) monsters has been a lot of work. I am looking forward to being able to look up the monster and just drop it in the campaign.