I agree, it would help to have a more organized article directly to this point.
The only difference in UE would be in the SQ. so, in that sense it is already covered.
There are UX differences beyond sound quality.
One example–in UPnP, if a new streaming service or file format hits the market, each endpoint needs a firmware update independently, and each vendor of endpoint hardware needs to make business relationships to make that happen. In some cases, patent licenses or royalty payments are involved, and in many cases, products are “left behind”. This can lead to situations where certain content can only be played in certain rooms (something we consider totally unacceptable because it makes it difficult for less sophisticated users to operate the system).
Another example–have you ever seen a UPnP based system where the zone controls, queue, transport, volume, etc stay in perfect sync across multiple remotes in real-time? I haven’t. We consider that kind of thing to be a basic requirement for releasing product, but UPnP is not built to the same standard.
There is no widely supported standard for doing synchronized multi-room playback over UPnP (AV 2.0 addresses it one way, OpenHome a different way, and AV 1.0 ignored the problem). If you intend to mix heterogeneous devices (multiple vendors + device ages), getting multi-room synchronization working ranges from difficult to impossible with UPnP.
There is some related content in this knowledge-base post–not totally directed at your point, but the “Why Not Decentralize the Core” section is basically a comparison with UPnP and similar technologies at the product architecture level.