If we're going off the usual Spurs model of buying potential World Class players that we can develop then Diawara would be near top of the list for central midfield along with Haidara and NDomebele.
Though I don't think a player can simply replace Dembele and what he brought to us - I think a change in formation is a way to get round the Dembele conundrum (433) and have said that for a while.
You've probably gathered by now I'm a 433-ista too. And those three would be right up there for me too.
Where we may differ is Dembele. I don't feel the same way as many do about him. I don't necessarily want him "replaced" like for like.
I like the fella, acknowledge he's got some outstanding qualities, there's been plenty of occasions Ive been glad he's out there, but I don't think he's been as crucial to "us" as others and I definitely don't always enjoy his holding onto the ball before triple checking it's safe to release it. There's been some games where Ive been glad of his unflappable nature and ability to take the sting out of things, but there have also been many games where I just want to see the ball won, then moved with a bit more vim and a lot more incision.
Like you, my ideal would be to see us pay a 433, with someone like Diawara central.