Forrester CMS Investment Analysis: Mark Grannan from Forrester has written an analysis of all the recent investment activity in the CMS sector. He has a nice recap of all the deals at the top:
The opportunity for market consolidation is coming. SaaS economics predict a “winner take all” outcome. While that theory is not without flaws, as we knock on the door of true-enterprise SaaS CMS, with all the benefits of multitenancy [...], the concentration of recent investments does support this thesis.
I agree there's a shakeout coming for the headless market, in particular. Some vendor will start rolling up smaller players, and others will just cease operations.
Grannan also reprints an interesting graph which highlights that that the lion's share of the funding has gone to companies with open-source platforms (Automattic, Acquia, WP Engine).