Talking with the arcgis geoprocessing team at UC yesterday -- they said that ArcGIS Pro beta 4 (python 3.4 of course) is shipped with an "internal" python install used by the app and a separate installer with python 3.4 that includes what Bill M was calling the "sci stack" which includes the modules used by esri (numpy, matplotlib etc) plus a another 300MB of so of other scientific modules (I think he said scipy, pandas, netCDF4) that aren't used by Esri but are useful to us.
The idea is they don't have the footprint there in a standard Pro install, but the group of users that will be installing this separate python installer are developers and can deal with the footprint and any issues they run into with these modules and not blame Esri. 🙂
This is great news. Hope there is a blog post coming from the arcpy crew soon! Maybe on the cafe?