@josh is our man for this.
Second problem I found ist that the Google Icarus Log only accepts ISRG Root X1 and not the cross-signed from IdenTrust. So I currently need to separate the process of adding the trust path because Icarus log reject my cert if I supplies more then one chain even if booth of them are valid and accepted from the log. https://bugs.chromium.org/p/chromium/issues/detail?id=632753
Here is the ECC announcement: https://twitter.com/letsencrypt/status/697504441075798016
But on Windows, Mac, Android and iOS I needed to trust the root leaf.