If you look at the players currently at the bottom end of the top 20, they have all stood out somewhere.
Isner and Querrey scored strong points in optionals last year.
Baghdatis and Fish added big performances in Cincinnati to strong results in optionals.
Ljubicic won Indian Wells.
Dolgopolov needs to practically double his current points to mix with these guys, and to do that he'll need to be able to perform more consistently at tour level, and go very deep in draws several weeks of the season.
Does he have the talent to do that? Yes. Does he have the consistency? Questionable.
His choice of scheduling after the Australian Open has been sensible...he should win a good number of matches on South American clay.
Australian Open R4 is a very good start for his ranking this year, but I question whether he can get enough decent results this season to finish top 20. If he can finish comfortably inside the top 32, he might have a better chance next year when he'd enjoy a better seeding (as arf suggests).
...and there is Dolgopolov's first stand-out result already. 360pts banked in just a single event. A very good start, and my prediction of top 30 looks a little conservative.