I have now tested this for Fedora 25, which also comes with PHP7.
I have rebuilt swig, using the srpm from Fedora, and then included the latest tar.gz from https://github.com/swig/swig/
Here are my changes to the swig package for Fedora 25:
Then I had to apply a couple of fixes to libkolab and libkolabxml, to use swig with the parameter -php7: https://github.com/TBits/lbs-kolab/commit/5e3f6ac43e5cf350af4c2802b2f2613e132f0f13
Now I can build libkolabxml and libkolab on Fedora 25.
Next step would be to do that in OBS. I have now enabled Kolab Winterfell for Fedora 25, but that does not have had any effect yet, as far as I can see.
@Schrubbi: you can try to do the same for Ubuntu. Get the original swig package from http://packages.ubuntu.com/xenial/swig, and build it with the latest tar.gz from git master. And then rebuild libkolab and libkolabxml, using similar fixes than I did for Fedora.