I was attempting to simplify the multi-version php setup I have in my small-scale server setup and noticed sabre needs PHP 5.4 and apparently doesn't run with php7 [1]. I wonder how much interest there is to upgrade that dependency at sabre. My un-informed opinion was that it's a good idea to move with your php setups.
[1] https://github.com/sabre-io/Baikal/issues/764