Five from the Eredivisie:
I think Martinez and Alvarez will surprise those who haven't seen them play, but if he can work his way into the first team, I think Perr Schuurs (19) will be Ajax' breakout candidate for 2019/2020. Holland brightest defensive talent who captained Fortuna Sittard to the Eredivisie at just 17; pegged as De Ligt's replacement and after a rather dull 2018/2019 season with Ajax II, he seems totally back on track.
Donyell Malen (20) from PSV. Went through the academy's of Ajax and Arsenal before making the wise decision of joining PSV. Malen is the reason PSV sold Luuk de Jong and how Lozano is now often benched. He's a trickery, fast paced winger with good ball control, but will likely play striker this year due to his goal instinct. I see him score between 15-20 goals and perhaps even double digit assists as well. He will make his Oranje debut this season as well, count on it.
Orkun Kökcü (18) from Feyenoord. Was very impressive as a 17 year old last season. He instantly made Feyenoord much more dangerous whenever he came on, yet van Bronckhorst was too cautious with him and preferred more experience. He seems to be the main man at midfield now under Jaap Stam. All-round CAM. I think he'll contribute a lot. About 10 goals and 10 assists wouldn't surprise me. Not sure about an Oranje invite. He represented the Oranje youth teams, but has hinted he likes to play for Turkey, where his parents were born. He'll make his debut for them this year.
AZ's academy has been sprouting out talents like no tomorrow these past few years, but their most notable ones might be Myron Boadu (18) and Calvin Stengs (20). Both already made their debuts last season, but both also had season ending injuries. Boadu is a striker in the Patrick Kluivert mold. If he starts, which looks like it, he could score 15. Stengs is much like Donyell Malen, but more of a true winger in that he's a bit more light footed. Both could make their Oranje debuts this season and are expected to be important pieces for Oranje in the future.