I could see it if they were trying to trade for a top 5 selection (i.e. Simmons, Ingram, Murray, etc).
Remember, though, that at this time last year the Celts were coming off a 1st round exit, and Isaiah was a fringe All-Star selection.
Given the team signing Horford to a long term deal, Isaiah making himself an MVP candidate, and the team going on a run to the ECF, one would have to assume the asking price for Isaiah is a lot higher than a lottery pick, even one in the top 5.
Isaiah is an MVP candidate like DeRozan is a third team All-NBAer - technically true but not really all that significant. This is the same guy that got low-balled into an MLE deal after averaging 20ppg and then got almost immediately dumped for a late first after playing well. He's always been praised and talked up and then when it's time to pay-up he doesn't get as much as you'd think.
His value has grown as a player, certainly since his last trade and also over last year, but his value as a contract has also decreased, so I expect his trade value to be significantly less than his accolades.
I think the best and most likely trade partner for him would be Dallas at #9. Dallas has always been a Danny go to for star-for-pick trades, from Toine to Rondo. Dallas has probably the biggest appetites for flawed stars in the league (Toine, JET, old Kidd, Chandler, Ellis, Rondo) and very little qualms about moving picks or dealing with upcoming contracts. Carlisle also loves scoring PNR guards.
I'd be keen on moving IT to Dallas for #9 and future considerations (with Barea as filler) for a chance at Zach Collins. Collins is going to a great big man.