To be honest i don't think Van Dijk would be amazingly good he would just be good for City not a massive improvement. As a Dutch City fan I've watched Van Dijk for Groningen Celtic Soton and the National team.
He is a great defender who is strong and has a crazy cross pass and shot however he also has brain lapses like Otamendi and Mangala where 2 times a game he completely switches off, IMHO he will also have alot of difficulties playing a extremely high line in Peps system because he isn't fast and he isn't agile.
Someone who would fit the bill is Davison Sanchez from Ajax although he has other issues he also has his occasional fuck ups per game but he is 20 to Van Dijks 25, I'm not sure about Sanchez' cross pass but it probably isn't the same level as Van Dijk and Sanchez' passing in general is not amazing but it is good and you can see him improving it still could use work where Sanches really shines is his pace, adaptability and tackling he plays a similar insane high line for Ajax and deals with it no problem as i said he'd be a good choice but maybe needs another year to develop if City feel the same they need to act fast though since Barca wanted him before he went to Ajax and are still interested.
I think Sanchez will be better then Van Dijk in a year or 2 and he is perfectly for the PL fast agile strong young and confident.
I'm surprised there haven't been links to Sanchez or even his partner De Ligt who will be amazing in a couple of years as well.