The bigger question is will they do this with Walsh or Queta. My guess is no for Queta? because doing so would cut into tax space substantially (the contract would certainly be more than Harper is getting). Walsh is a restricted free agent if we decline his option, however. Maybe they would give him a medium raise to lock him in for a few more years, although I personally do not think he has shown enough. That is a more likely option if Jaylen is traded this weekend, since Walsh has a option possibility on Monday.
Yeah, I root for Walsh, but he's a fringe NBA player without a ton of expected upside. Those generally aren't the types of guys you extend, unless he's willing to take a multi year deal near the minimum with team options./ non-guaranteed salary (sort of like Svi's deal in Utah)
I am a little higher on him, but not a lot. He is young, and had he stayed in college rather than entering the draft could have been draft eligible this year. And he did take a real step forward the last season on offense, getting up to a .623 TS% compared to his .466% career number entering the season, on a lot more attempts. His defense always has been and remains his strength. At the same time, he could not separate himself from Gonzalez or Scheierman, although nor could they from him. If the Celtics think he has more growth in him (and they see him more than we do), getting him for $5-6 million a year now could be a coup if he takes another step.
Look at how the Celtics extended Pritchard coming off his third season a few year ago. He had been not good that year. Now that has become one of the bargains in the NBA. Walsh definitely has the potential to make a similar deal, or slightly smaller, a similar steal.
I definitely would not do it if we needed the tax space, however. Only if we could afford an extra $3-4 million this year.