Skille and Matthias both played briefly overseas. Skille's contract was just until the Dec 31st anyway so his time in Europe was never suppose to be long. That said, he was playing decent in Norway but had to leave because a death in the family and never returned. He was practicing in the New York area at one time with Sid the Kid and others.
Matthias suffered an injury, I believe a concussion, while playing in Austria. I believe he was injured fairly quickly into his contract overseas too.
All 3 players are not eligible for the AHL because of their contract status and amount of games played professionally. Also, keep in mind that the guys that did go play over in Europe during the lockout have to pay their own insurance so that can be quite costly.
As far as projections or what is holding that back, I think all three lack in the hockey IQ department. That seems to be what has always been their problem. That is something thats hard to change too.
Skille has also been injury-prone so he's never hit his stride because of that either. That may be a product of how he plays because he's a physical player who likes to hit. Matthias played better last yr but wasnt consistent down the stretch. I think both Skille & Matthias are 4th liners for the near future.
Ellerby has more skill than both of the other guys but just hasnt put it together really. He's always been known to be a defensive d-man with good mobility so maybe he can eventually develop into a #4 d-man. But I think right now he's probably destined to be a #5-6 guy. In another org, he may get a better chance to become a #4 but dont see him being more than that honestly.
You should check out the lockout thread we had for what was going on with Skille & Matthias:
http://hfboards.mandatory.com/showthread.php?t=1268815