That makes it an interesting scenario. What are the stipulations to the stretch provision & why hasn't CHA used it?
There aren't any restrictions per se; however there are rules regarding how the strech/waive operates depending upon when the player was waived. If we traded for Batum, we'd be waiving him prior to the start of the season, so, we'd operate under the more favorable ruleset.
Overall, this would mean that we would take back Batum's remaining 3 years, where he's averaging right around $26M/yr. Stretching Batum turns his contract into a 7-year cap hold (numberOfYears*2+1), and then we divide the number of years into the salary remaining.
So $75M/7Y = $10.7M/yr...
Now, if you're a team above the cap, and you've just signed Paul George, LeBron James, to 4-year deals, and you expect to sign Kemba to a 5-year deal; then you're likely not planning on tanking for the next 4-5 years... It also means you'll almost assuredly be over the cap so you wouldn't be able to use $10M in cap space anyway -- you're more focused on mitigating the luxury tax if anything...
And with that said, considering the repeater tax, adding $10M in salary makes having bad contracts like Thompson, Smith, Clarkson and Hill all the more difficult. We would probably need to stop taking back overpaid players and also stop handing out our own share of bad contracts to the league.
However, if you're Charlotte, you're very likely hoping to go below the cap, to help your rebuild by taking back contracts for draft picks, and facilitating trades (just as the Cavs did during our mini-rebuild with Kyrie). So having $10M in dead cap space would fucking suck.
This is also true for a post-LeBron Cavaliers team, FWIW.
As far as why the Hornets haven't done this; it's because they don't want to be on the hook for Batum's salary while he plays for another team. They would hope to trade him first, rather than committing to the full $75M in guaranteed salary that he's owed via stretching his contract.
It's a radical move, to be sure -- but one the Cavs could make if it meant reshaping the team and getting Kemba without giving up a major asset.