Visio is among primary process mapping tools, especially in small companies, although it is rarely mentioned even by Microsoft itself. Definitely, extending Office365 in this direction will incredibly simplify adoption of BPM by SMBs.
There is subtle and easy to miss boundary where ad-hoc processes of a successful SMB are requiring streamlined BPM refactoring to allow the company grow bigger. In too many cases this transition causes a full scale crisis, which not all companies even survive. This is why timely BPM adaptation by SMBs gets especially crucial. It is so easy to miss the right moment. No doubt, wider BPM integration into Office365 gets a crucial factor in achieving this goal.
I suppose that main deficiency of Office365 in terms of BPM and, especially, BPM for SMBs, is not even in tools as such, which are polished to near perfection, but in an absence of well developed and ready to use methodologies and best practices in a form of ready to use Office365 templates specific per industry and business type. This vacuum of available standard methodologies creates a huge adaptation barrier for SMBs, which cannot afford expensive consultants for development of their individual BPM strategies.
Ready and immediately efficient process patterns are cornerstone in SMBs acceptance of BPM in general. I suspect that Microsoft already moves into this direction with their Microsoft Flow integration cloud, where simple typical process patterns are already available out of the box.