For any future updates, it would be great if you could draw or design your own destruction lines. Say if you want sponge like material blocks, you could do that.
I would suggest checking out this new destructible mesh editor thanks to Jason Maskell!
And accompanying blog post: http://tamedtornado.com/introducing-the-new-destructible-mesh-editor-for-ue4/
Jason is planning to release his work on this FREE! to the UE4 community via Pull Request when it is done and I would suggest that you provide him with some feedback regarding additional suggestions for features like your one above.
NOTE: Jason has created a pretty neat slice tool which might partially or fully fulfil your needs on the subject
While there are no plans at the moment for Epic to integrate the full PhysX Lab into UE4, the link above is an example of the community doing some of the heavy lifting to get something like this into the editor. However, this does not guarantee that it will be integrated into the engine. This will be left up to the developers and the willingness of the user posting the pull request to work with Epic to make it fit our standards for code submissions and usability.
Personally, I would love to see the PhysX Destruction fully integrated and I am hopeful with the work started by Backov.
If you need the functionality of the cut and slice tool right now you can you use PhysX Lab from Nvidia to make that work in your favor.