Cased covered all the big names but there are a couple notable GSC dudes flying under the radar so I'll highlight them here.
Melle2402 - Sweaty palms aside, he's consistently improving and usually not afraid to make that big risk/reward play. Trends toward standard in important games but can think outside the box too. Biggest problem is the mental game, just needs to keep a level head when he's down but not out. Could be a great pickup and knows all the old gens to a decent extent for general team support.
Hyogafodex - Surprised he's not already in the conversation, I've played him plenty of times and he always seems to know what he's doing. Very Earthworm-esque at times with his methodical long term planning leading you into a false sense of security until he clicks something insane and wins the game before you notice it. Been around for ages and is definitely ready for the big stage. Again, plenty of experience in other old gens here.
k3nan - This guy had a rough debut last year, but it would be way too soon to write him off. He's posted consistently solid results since then, including a DPP Cup finals and Classic playoffs appearance. You'd expect him to slot in DPP or maybe bounce around a few old gens but I still think he can cut it in GSC if he starts playing with a little more inspiration and builds his own stuff instead of jacking teams that are years old. And once again, clearly proficient in other old gens, could be a real juggernaut.
Picollo - Can't believe he's still around, a netbattle relic on display. Not sure how up to date he is, but back in the day he always showed up with respectable records in SPL. Could be a risky pick in terms of motivation, but compensates with more experience than anyone else for the price.
Slick Willy - Deserves a trophy for the username alone. Really friendly guy and not half bad at the game either. Wouldn't go so far as to start him on opening week but he's shown potential and is a fantastic chat presence.
Don't really care if this helps the managers or not, I'd just love to see all these guys find a home this SPL.