If it's bleeding edge you want, go to
Olivier Banus' PPA page on Launchpad
and download/install the xenial version of his PPA. There is also a wily version and a couple of historical versions.
Launchpad is where the Ubuntu developers have their build farms and testing facilities. Olivier, posting as "sunab", has posted to this forum three times.
I am using his xenial version and can verify that it runs. As of this writing, it was compiled on July 1 from the sigil git master as it stood on June 28. It is identified in the git change log as preSigil-0.9.7
Also on launchpad in a different account, Mattias Rizzolo is working on preSigil-0.9.7 for yakkity alpha1. While he has a PPA listed, there are no other versions available.