So, the new proposal:
There would be a "top level" outline policy - a small number of browsers are supported (i.e., WMF will keep spending money until they work):
- Desktop: Current and immediately-previous versions of Chrome, Firefox,
MSIE and Safari
- Tablet: Current versions of iOS/Safari; Current and immediately-previous
ones of Android
- Mobile: Current versions of iOS/Safari; Current and the five previous
ones of Android[*]
Anything not in this list may "happen to work" but WMF Engineering will not spend resources (read, developer time) on it. If a volunteer is willing to work like hell to make, say, the VisualEditor work in Opera we would try to support them by reviewing/accepting patches, but nothing more than that. It doesn't mean we would go out of our way to break previous browsers as they leave support, but we would not hold ourselves back from useful development solely because it might break browsers that we've actively decided not to support.
"Support" is a very vague term. I think we need to recognise that, in reality, we will support different browsers to different degrees. There is a big difference between "everything works exactly as intended" and "you can read articles with no noticeable problems, but some advanced features fail gracefully". Your list may be appropriate for the former, but we should support significantly more browsers (the 0.1% threshold, perhaps) at the latter level (which probably won't involve too much work, as long as you're happy to just blacklist things if they're not easy to fix).