I think PRO = xD regardless of sensor size. From marketing point this makes more sense.
Prosumer & Consumer = mirrorless, xxxxD, xxxD or xxD. Again regardless of sensor size.
That is a fair way of doing it, however that would mean
- 7D would have to be renamed
- 5DII would have to be renamed
- 5DIII might have to be renamed
and I dont think that will happen
Traditionally the only pro cameras have been the 1 series
The single digits have been the semi pro
The double digits have been the 'enthusiasts'
The triple digits for the 'hobbyists'
The 4 digits the entry level
By Pro I mean anyone that earns a fair bit of money from their photography. Be it full time (pro) or part time (semi-pro). Also, Pro can also refer to ruggedness and overall ability.
From where I am sitting, the 5D is for sure a Pro camera. I think it is safe to make an accurate (yet unsientific) conclusion that most Canon wedding shooters use that cam - thus it is Pro. And from what I am reading, a lot of sport guys are using the 7D.
For me, there is a distinct difference between Pro and Flagship. The Flagship cam will probably be Pro, but not all Pro cams will be flagship.