I do not think him replacing Busi would be a very good idea under present conditions. I'd rather get a stronger DM, in the Yaya Toure mold, and use Arthur and Frenkie next to him.
His license to move from his position and attack space under Valverde as a DM will be virtually non existent. Some of his biggest traits of his game would remain hidden in that positions.
People need to understand that, the more rigid a system is, the more it reduces players to the core qualities traditionally associated with that position. Without fluidity and freedom of movement, prime Busquets is a worse defensive midfielder than Makelele, Casemiro, Gatusso, Essien types at their peak. Because many of the things Busi is much better than those mentioned at would never get the same exposure under Simeone, Mourinho, Valverde types, as it did under a proactive, total-football fanatic like Pep.
Players like Busi and De Jong bring a lot of technical qualities to that position that are left largely unused without playing fluid football where players are allowed to move in and out of space.
And issue is fluid football and Valverde are like water and oil. They don't mix. De Jong is only 'good' at defending. You can find better and more physical DMs for that who can still be decent passers.
People who say De Jong is the next Busi forget that if Valverde ever had to choose between Yaya and Busi at DM back when that was the choice to make, he would've chosen Yaya no doubt. Hell, If we had Ernie in 2009 chances are we wouldn't know the name Sergio Busquets very well today.
The profile of Toure fits the system Valverde uses better than that of Bus/De Jong. People need to realise we're playing a football where core qualities are more important for a position, than being well-rounded or having many secondary skills. Those types of things become much more important when you add off the ball movement, which we have abandoned since Guardiola left more or less. When the movement is low, the main, traditional qualities tied to a position are the most important.
Core qualities for the DM positions are good strenght, great workrate, very good tackling ability and use of the body to stand off opponents. Whatever DM we play under Valverde is better off with that type of main qualities. Busi has neither arguably. How many of those does De Jong have?