Sakurai is way too creative to let that stop him. Plus PSASBR did it with Heihachi, and they represented him rather well. Really, the 2D-3D fighter destination is as rediculous as saying Bayonetta can’t get in because she’s in a 3D action game. Not to mention how different smash is now compared to back then.
And if PSASBR isn’t good enough evidence for you, then look to Street Fighter x Tekken for another example of how a Tekken character could easily translate to a 2D fighter.
The thing is with Tekken, moving into the foreground and background is a really non-essential part of the fighting, to the point that giving him some sort of special dodge like Terry would fill in adequately. The thing to replicate with Tekken's fighting is that every button is a limb, and combos are about chaining strikes from each limb together, rather then doing gymnastics with the analogue stick. Most special moves that use stick movement don't really flow into combos. They're more like deadly specific strikes. I could easily see Kazuya or Heihachi or Jin or whoever having a Min Min like system where the A Button is punches and the B button is kicks, and they both function like neutrals with tilts and aerials and smash attacks and the like, with the up, side, and down specials replicating those very deliberate combo adjacent special moves. There, you've captured the most essential part of Tekken's combat. Or do it some other weird way. Either way, it's not as impossible as Sakurai brushing it off in an interview makes it seem. Remember Ridley? Remember Steve?