Enterprise Linux was getting going for real in the late 1990s but in my view it was more 2005-ish that it became "mainstream" in these sphere. Sun Computer for example started to support Linux in 2006 and was a Hail Mary to try to save itself as SunOS was being eaten away by Linux.

Redhat Inc became part of the Nasdaq-100 in 2005.

I make this comparison as the question is whether OpenStack still has the potential to become a full go-to alternative in the way that clients consider closed cloud systems from AWS/GCP/Azure as substantial equivalents.