Unlikely. Just better to trade for him now. Especially since to sign him you basically can't have Smart, Thompson, Fournier, Williams, Williams, Horford, and maybe Langford.
Much better to just acquire him centered on a package of Smart, Thompson, Langford, R. Williams, and future picks. Then you get to save Horford,, Fournier, and G. Williams to actually build a real team. You also can then give Beal more years and more money making it far less likely that he would actually leave.
Except that Langford, Nesmith and Robert Williams are the guys that matter for the long term. Horford, Fournier and G Williams do not. Keeping Fournier and obtaining Beal (or anyone other than a center or point guard that starts) effectively deletes any future on the team for Langford and/or Nesmith.
Robert Williams is either a top 10 center, or a dead weight. I have to believe there is a way to save him and find that out.
I think going for Beal is a mistake, but it is better to consolidate around youth and picks than it is to trade for him. I'd rather have Beal and Langford and Nesmith than Beal and Fournier.
In order to sign Beal outright, Robert Williams almost certainly would not be on the team and it is quite possible that Langford would also need to be gone. There just isn't an easy way to make the room for Beal, with both Brown and Tatum on the team, without basically gutting the roster. So, if you are basically gutting the team to sign him outright, Boston is just much better off trading for him this summer when it can use expiring contracts of Smart and Thompson as the money, a young player or two, and future draft picks. Not only do you ensure you land Beal, you get him for an extra year of his prime, and you can save way more of the depth of the team to acquire him. If by some chance he leaves next summer, well then you have basically max room to sign a different free agent if you let Horford go, but I suspect Beal would end up signing a 5 year max, taking him through his prime and hopefully encouraging both Tatum and Brown to stay past their existing contracts.
Beal, Fournier, Brown, Tatum, Horford is a superb starting 5 and there is some quality young players and depth on the bench in Pritchard, Langford or Nesmith, G. Williams, Parker, Brown, Edwards and then possibly Ojeleye and Kornet. Even if you bring back the latter two, there are still 2 open roster spots to land some veteran minimum type players. Maybe Love if he gets bought out (as an example).
You don't put off till tomorrow what you can do today.