Not a max, but I'd be ALL for throwing a giant chunk of money at Marcus Smart. I see him as an absolute flawless final glue piece to a Fox/Bodan/Buddy/Doncic wing core as a guy who can defend the 1-3 at a high level and bring a level of toughness and energy on both ends of the court we just don't have on the team right now. He's just a flat out difference-maker on the defensive end on the wing, something that's next to impossible to find anymore in the NBA and that versatility for him to guard the best wing player is really valuable.
There's also this:
https://www.sbnation.com/2017/12/6/...shooting-stats-terrible-celtics-offense-works
Now, the offensive splits didn't quite work out that drastic obviously, but the Celtics offense ended up having a +0.3 ORtg better with Smart on the Floor than with him off. That might just be statistical noise in the end, but there must be something to the above article considering how bad Smart is as an individual offensive player. But it's not showing on the team level, which is pretty damn sweet for all the positives he brings elsewhere.
I think something like a 4yr/56 mil contract to Smart would really put a lot of pressure on the Celtics to match. Horford and Hayward maxed for 2 and 3 more years. Kyrie has only 1 more guaranteed year then has a Player Option to opt out. Rozier needs an extension next season. Brown has 2 more years on his rookie deal before he gets a massive raise. Smart just might be a casualty for the Celtics that we can capitalize on.