Jim Parson is versatile enough as an actor to pull it off, coupled with CBS would love to have the series an instant hit with at least one star pulling in viewers.
I wouldn't say he is that versatile of an actor. Seems to not stray far from Sheldon in the few roles I've seen him as. I could see him as Spock though.
We's so glad that good actors don't stray from rooted characters.