My brother and I expected something to be up about the questions people (including myself) asked at Brandon's panel at FanX this weekend, but I guess I can post them here.
Q: Could you use Hemalurgy to steal Surgebinding?
Brandon: Absolutely, you could steal Surgebinding with Hemalurgy [smiling]. [Note: Not surprising, considering the comment in the Mistborn Ars Arcanum about Hemalurgy being the most interesting to the cosmere]
Q: Is it only Greatshells that have gemhearts, or do all crustaceans on Roshar have some sort of gem inside? If it is only greatshells then are their unique decayspren related to this fact?
Brandon: It's a matter of body chemistry. Not all crustaceans do have gemhearts, but most can, not just greatshells. It's a matter of their particular body chemistry that lets greatshells grow the larger gemhearts, which is what allows them to grow so large themselves. [Note: This is pretty close to exact wording; I transcribe for a living so I have an excellent memory for wording, but I didn't record it so I can't be sure]