"stalled under /opt; this rule complies with the filesystem hierarchy standard and prevents file conflicts with the rest of the distribution. The problem, according to David Planella (one of the authors of the proposal), is that a lot of things just don't work when installed under /opt"
I really don't buy that.
I've been installing proprietary software into /opt for years and on the Free Software front built and installed software as complex as all of KDE's products into any number of prefixes.
Heck, during development I even run make install as a non-priviledged user, into non-FHS trees and even under $HOME.
The more I think about it the more I believe their observations are based on their application launcher failing to provide the appropriate environment, e.g. properly expanding $XDG_DATA_DIRS and friends.