I saw the issues about windows being generally broken. I sympathize with the team's plight having been there too many times with cygwin and git bash over the years. FWIW I think the best approach is to normalize the path references back to unix format as fast as possible. The approach of mapping driver letters C:\ D:\ to /c and /d etc is reasonable. Beyond that there is the usual handling of spaces and () {} etc to consider where php/bash might get confused.

We have a large user base using various install locations on their PC's. The issue has come about following a recent upgrade from a 2015 version with more than one person affected.
If you look at the code I cant see why you would need write access - it is just processing path strings.
Anyway I have moved the install to your suggested directory but with no change to the fault symptom.

For issues with Ubuntu 16.04 LTS and acpu with PHP7 giving rise to "apc_sma_info() not found" Exceptions then you could install backward compatibility library package php-apcu-bc_1.0.3-2_amd64.deb using dpkg once downloaded from future Ubuntu Yakkety release universe repository. No doubt this deb will get back-ported to 16.04 LTS soon enough assuming phabricator itself isnt updated to no longer reference this missing function.

The same problem exists in git and I have the same issue over acceptability of my users who happen to be familiar with ReviewBoard.