Roughly when is Winter expected to be released as a beta feature and as the default skin?
Topic on Talk:Winter
I don't know. I don't think there are any current plans for anyone to do that work, sorry.
IIUC, Winter is not ever intended to be released as a Complete Skin, or a Beta Feature. See Winter#The Winter Framework - it's a test-bed for people (anyone) to experiment at.
What does any of this experimentation achieve, if there is no intended future for Winter? Is it to build a resource for whichever actual skin will be made in the future? My life is a lie.
The elements ("snowflakes" in Winter's terminology) can potentially be deployed as either new elements of the existing skin(s), or as standalone BetaFeatures that could also eventually/potentially be merged into a skin. E.g. at http://en.wikipedia.beta.wmflabs.org/wiki/Special:Preferences#mw-prefsection-betafeatures we can try out the "Fixed header" BetaFeature.
Right, so what about Right Rail as a BetaFeature? It'd be highly useful for designing wp, help, portal etc. pages, not to mention obvious advantages concerning the main ns.
I'm not sure how much work would need to be done (as the note on the project page says, "This is fairly large in scope."). There are currently no developers or product managers with the many needed hours to spare. All I can see offhand (but I am not a developer) is https://git.wikimedia.org/tree/winter%2Fsnowflakes/HEAD/rightrail
However, Pau is working on some interesting designs for modular rightrail components in Flow (nothing online, yet), for metadata and checklists and similar, so that might be where the work re-begins.