This great blog post by Drew Flater on ArcGIS Blogs outlines the process of manipulating ArcGIS Pro's Quick Access Toolbar (QAT) to create the old familiar Standard and Tools toolbars from ArcMap. I loved it and thought it was a great post. Toolbars like this go a long way in making Pro more familiar for veteran ArcMap users.
While the post demonstrates that the concept of ArcMaps traditional toolbars in ArcGIS Pro are possible to some extent, there's a big limitation. You can't have multiple QATs and QATs cannot float or dock within the ArcGIS Pro window.
I think it would be very beneficial in reducing the Pro learning curve if Esri supported multiple, floating QATs in ArcGIS Pro then additionally released a Pro Addin and/or Configuration which would set the Pro Ribbon to hide and allow users to open, close and dock the various QATs defined in that Pro Addin/Configuration, similar to the way toolbars are handled in ArcMap (eg. one QAT for Standard Tools, another for Layout Tools, another for Spatial Analyst tools, etc.).
In reducing the learning curve for Pro and making it more familiar to veteran ArcMap users, Esri might see increased adoption of Pro when these more experienced users begin to see that the differences between ArcMap and Pro are not as great as initially appear to be.
This idea has been marked by Kory Kramer as a Duplicate of ArcGIS Pro: Option to Enable Dockable Toolbars and Menus Please go to that idea for voting and comments.