I also took a similar stab at next-gen of SaaS few months back:
http://www.laktek.com/2017/01/11/end-of-the-first-wave-of-sa...
http://www.laktek.com/2017/01/11/end-of-the-first-wave-of-sa...
I'm more skeptical than you guys about the Saas/cloud "plumbing" space. There's lots of open-source software out there and I think that value extraction – largely from PMs and devs – will be tough.
BTW, good call on Slack becoming a unicorn. ;)