The future at SS is pretty bright. The Cubs' minor league system features a consensus Top 20 prospect (albeit one with a low floor), an organizational Top 15 prospect (albeit one with a huge issue), and a guy that has incredible tools (though SS might not be his final destination). Without further ado, lets get to it.
The league average SS had a wOBA of .300 last season.
Starlin Castro is the real deal. 2012 was arguably his worst season as a professional: he was still 7th among qualified shortstops last year in wOBA. He turns 23 this year: we are lucky to have him. Sure, he could walk more or commit fewer errors, but there comes a point when you just have to accept that Castro isn't perfect, but he does a ton of things very well, and he's improving as a player in many areas.
Only Matt Tolbert's parents care about Matt Tolbert. He's over 30 and can't hack it in the PCL. I can't find information regarding his status with the club: I'm assuming he's gone, and he should be.
Junior Lake is a curious sort. He's got incredible tools (the only 80 arm in baseball, according to some scouts), and he's generated some pretty decent numbers in his slog through the minors. The knock on Lake is his apparent inability to hit a baseball (or field one, either). He's got Brett Jackson-like strikeout numbers, but he doesn't walk like Brett Jackson does (though his walks aren't always completely terrible). He's been in the Cubs' system for 5 years now and only made it to AA: some people thought he was going to beat Castro up to SS and that obviously hasn't happened. He should break with AAA this year, maybe at 3B, and have one last year to put it together. Their is clear talent there, but it may never materialize. (Aside: I saw him play in person once during the 2011 season. He looked like complete dogshit, for what's it's worth (almost nothing.)) Elliot Soto is an afterthought, as many who can't outslug their OBP are.
Arismendy Alcantara showed some pop last year (.145 ISO) and some speed (24 SB), two parts of his game that are relatively new in the toolbox. Alcantara is cutting down on the strikeouts as he ages: this is a good thing, because they were at a terrible rate. Arismendy does not walk nearly enough to get by, so he'll really need to cut down on strikeouts if he wants to play in the majors some day. He's moving in the right direction; an increase in his walk rate would elevate him to the next level of prospecthood.
Javier Baez is the real deal. He annihilated A ball this year, with an absurd .263 ISO and .432 wOBA. Just for shits, I put in his Peoria numbers into a MLE generator, and his line was .235/.269/.377: that OPS is basically Yunel Escobar or Alexei Ramirez or Stephen Drew. He can definitely field SS: the reservations on that have basically been laid to rest. He's no sure thing, and he did struggle in a late-season promotion to A+. I'm not at all worried about that, though: his BABIP in A+ was .200: his walk numbers were actually up (and his K%), and his power was still a very nice .213 ISO. There are whispers that Baez could just start 2013 in AA. I'm not sure I like that (Alcantara deserves to start there), but it would be a nice sign that the Cubs FO is as in love with Baez as we are.
Marco Hernandez is an all-glove prospect. He draws rave reviews for his defense, and in A- he even hit fairly well (he puts the ball in play with alarming frequency). The wheels fell off in a promotion to A ball, and he's got plenty of interesting prospects in front of him. If he grows into his size, he might get some more power (he has some already) and be a really interesting piece; if he doesn't, he might end up on a major league roster some day as a backup middle infielder.
None. Hernandez was here, and got promoted. Stephen Bruno is a 3B prospect, to me.
Carlos Penalver actually has quite a bit of data on him (516 PA over two years). He's shown an ability to take walks and put the ball in play… but he has very, very little power (see Elliot Soto for my thoughts on people with OBP higher than SLG). I can't pretend to know his body (6-0, 170, so he'll likely grow into some power), but it has to be encouraging to see a 19-year old with his plate discipline. He's still a few years away from being in the periphery.
There are some huge talents here. Baez is the #1 prospect in the organization. Alcantara and Hernandez or almost certainly in the Top 15, and Lake has more tools than both of them (and might be in my Top 15 or so as well). All of this is moot because the guy in the majors is already a franchise cornerstone. SS is one of the hardest positions to fill, and the Cubs are absolutely loaded with prospects there (even if Baez ends up at 3B (which I doubt unless it's because of Castro), Lake ends up at LF, and Alcantara ends up at 3B) . Get happy!
AAA: NRI (Lake will play 3B, likely?)