Sure. Call me on it when it happens. Their cap space this offseason is predicated on IT's current $7M/year deal and using his Bird rights to extend him. They'll have to unload Bradley or Crowder along with IT to trade for Butler. They'll need to throw in next year's BK pick at a minimum to sweeten that deal. (Chicago doesn't need an undersized PG approaching 30 years-old, or Avery Bradley for that matter.)
https://www.espn.com/nba/tradeMachine?tradeId=l7abcgz
Now the Celtics have Hayward, Butler and Horford as their Big 3 (all maxed), plus whoever's left between Bradley and Crowder, Smart, plus a few rookie-scale players. At that point, their cap space is gone. They still can't rebound or defend, and they're not likely to beat the Cavs because they're not well put together. Olynyk isn't extended. Bradley is gone the following year.
Three years from now, Horford turns 33 and his deal expires, Butler has a player option and likely will be seeking a max extension. Thus ends the window of this supposed dynasty. You'd better hope that Fultz and Brown turn into impact players in a hurry. The Celts will have spent their last BK pick (assuming Chicago will take the 2018 pick in the first place).
The minute the Cs decide to trade IT, they turn their most efficient asset into a liability. Hayward/Butler/Horford and 20 year-olds is more likely to be the Toronto Raptors than a real contender.