FTR, I think Slater is a grub in defense, and his leading with his foot is NOT ok, neither is leading with the feet on ground.
That said, the argument that any player getting hit steaming in, would be making a legal tackle, is absolute bullshit, because there is no way Slater is back on the ground before being hit, which would make the tackle not only illegal, but very dangerous.
On the other hand, if it's Slater hitting a player, because he jumped forward with his foot up, send him fucking off. (yeah, won't happen)
I would lead with my knee for sure though, and if anyone came close enough to make an acquaintance with it... tough luck, better you than me!