No way I'd trade Brown straight up for Beal (if the dollars even worked, which they don't). That said, I wouldn't mind Beal here.
Beal for Brogdon, Rob, Pritchard, 24 1st, 26 1st, 28 1st (top 4), pick swaps in 25 and 27
That is a pretty solid rebuilding trade for the Wizards given the draft picks, Rob, and Pritchard. They could move Brogdon for at least a couple of 2nd's if not a 1st (especially if they kept him a year)
Post-trade Boston with several open roster spots
Starters - Smart, Beal, Brown, Tatum, Horford
Bench - White, Hauser, Grant, Gallinari, Muscala, Kornet, Champagnie, Davison
Team obviously needs another quality big, so I'd try to move White or Smart for a similar level of player that is a big (maybe Collins from Atlanta). Or maybe a Brown for Towns type trade comes to be. Just need another move to balance the roster more, but if you could get Beal while keeping Brown and Tatum, you have to do it.