You can listen to the podcast for some details, but to clarify the twitter discussion between Lydia and I, Lydia has clearly stated that OpenStack simply has "Narrow and specific use cases" (see https://twitter.com/cloudpundit/status/725703809574535173).
I responded by asking her for any Gartner research to support that claim since OpenStack has a very diverse list of customers and use cases (see https://www.openstack.org/user-stories/) and 451 Research has actually done the user research Lydia claims is "extremely difficult" (see https://451research.com/report-short?entityId=87456).
For me, the bottom line is that Lydia's opinions about OpenStack are not based on actual research that Gartner has done on users (there is no Gartner published research on user adoption). Alan Waite (from Gartner) has published reasonable and nuanced opinion's about OpenStack but it isn't user research.
As I tweeted to Lydia, OpenStack may or may not be a huge success, but we need good research to make that conclusion and Gartner hasn't done that yet.