My prediction is that the 2024 DMG will not have variant rules.
Historically, most DMGs never had variant rules.
The only reason they were in the 2014 DMG is because the explicit promise of 5E was that it would support the playstyle of your favorite edition. At that time, WOTC was justifiably desperate to move past "the edition wars" and get all previous D&D players onboard the latest version of the game.
In reality, 5E never delivered on that promise. Yes, it had variable levels of complexity -- the champion fighter is simpler than the battle master fighter. But the battle master never delivered the tactical complexity of 4E just like the champion never really felt like it came from 1E. Both of them fell within the spectrum of 5E.
The variant rules in the DMG were a rather sad vestige of "modularity", half-baked and half-hearted and half-functional.
Fortunately, by the time 5E was published, it delivered something better than modularity -- a polished D&D experience without the fatal flaws of previous editions, simple for noobs to learn, but with enough complexity to keep veteran players engaged.
In 2024 it's an easy choice to leave variant rules on the cutting room floor.
So if you want to find variant rules, don't look in the 2024 DMG. Look at Level Up. Look at Tales of the Valiant. Look at Shadowdark. Hell, look at 13th Age and Shadow of the Demon Lord (or Weird Wizard)! Those great games are full of inspiration for variant rules. You can loot ideas for your 5E game or even just, you know, play them. I do both.