I version at the sequence level, rather than the project level. It would be great to be able to lock a sequence as soon as I've exported it, to keep me or any other editor from making changes to it. I know that I can lock each track individually, but I'd like to be able to preserve the track lock state as something other than "total lockdown," as well as having a single-button option to lock/unlock sequences, much like you already can at the project level (with the green project lock icon).