Shipping it in its current state does seem premature. The spec still hasn't addressed a major concern from rendering library authors, which was that an explicit check to see if a node is connected is now required to branch between using moveBefore or insertBefore, since moveBefore throws if used to place a disconnected node.
According to the spec it throws in the following cases:
Parent - Moved Node
disconnect - connected
connected (Doc A) - connected (Doc B)
connected - disconnected
The last one is the most concerning one. Most of the top performing frameworks do child node reconciliation something like this https://github.com/WebReflection/udomdiff/blob/e58db3ad28b72.... Each node could be unmoved (no-op), new (disconnected), or moved from within the parent (connected). Now if one wants to leverage moveBefore each of these nodes needs to be checked for it's connection state.
