Since some of us don't use Slice Machine or NodeJS on the server, it would be fantastic if you could make the new UI greater for the users who:
1: are only seeing "Legacy slices". My suggestion is that you check if there are 0 "new" slices, then just show the Legacy slices by default (to avoid both the extra click and avoid the negative sounding of "legacy").
2; are not having live-preview enabled. Either allow for a thumbnail or make that grey box much smaller, so it seems intentional. Alternatively for new slices you can use the slice's thumbnail here (the same you see when selecting a slice.
3: don't show the "Preview your Slices in real time" to the user - they can't do anything with this and think the developer did something wrong in the configuration. For some frameworks and tech the live preview is simply not an option, so I want to remove it from my clients' UI.
This would make the editing experience faster and better looking. It would also make the customer feel secure, because they are not looking at features that haven't been implemented and not looking at "Legacy" stuff, because this has a negative sound to it.