A 2017 opening day infield of Rizzo, Baez, Russell and Bryant seems like it might be pretty good.
I guess this means they move Castro in the next two years.
		
		
	 
Makes me wonder if they they have changed their view on Baez. Castro has played second before, right?
Or they can always move one of them to the of.
		
 
		
	 
 I don't recall Castro being anything other than a SS in the Cubs system.  He shot through the system very quickly and I don't believe the previous regime gave thought to other positions.
The first "future core" hitter up will be Alcantara since he is already on the 40 man and is currently mashing AAA.  He was a SS but was shifted to 2B and now is getting time in CF this season.  He will be the Cubs starting 2B and/or CF before the year is done.
Bryant is the next logical call up but that won't happen until next season.  The desire of Cubs fans is that he is in the opening day lineup but we will see if the Cubs make him get his "500+ pa's" in AAA and avoid super two status.  Since the Olt experiment has been a failure and Bryant has reportedly impressed at 3B, he should be their 3B next year.
Baez has struggled this year but it appears he might be turning a corner.  He has a 9 bb / 10 k ratio the last 10 games and apparently the promotion of Bryant and the influence of Manny are rubbing off on him.  We will see...  He still has the highest potential of any Cub prospect at the plate but also some Rob Deer 30 hr/200 k.  He played some 2B in spring training but nothing other than SS at Iowa.  I don't see him pushing Castro off of SS and I think that the reason he is still at SS is because his bat isn't pushing a promotion.  He is either a future 2B, 3B, or possible OF.  I think the will be at 2B in Wrigley early next year.
Russell will spend all of 2015 in the minors between AA and AAA and probably will see Wrigley mid-2016 at the earliest if he continues on his path.  He is the best defensive SS of the current crop so he could be the one to push Castro.  If not, he will push Baez off of 2B.  It will be a great problem for the Cubs to have if all 4 are starter level contributors by the end of 2016.  I suspect that unless a trade is viable to improve the team, either Bryant or Baez will be moved to the OF.
The Cubs will also have legit prospects Almora (CF), Vogelbach (1B/DH), Soler (RF/LF), and Schwarber (LF/C) in AA or higher next season among other interesting prospects who could see the majors.