^
To quote a friend of mine recently, describing a recent pub refurbishment nearby...
" it's all gone a bit heirloom tomato and lumberjack in there "

I admit it's a bit 'Brideshead Re-marketed' but Old Town do have some nice stuff in really good fabrics...
http://www.old-town.co.uk/collections/product

It took me nearly 40 years of existence to discover ivy, then several more to work out how to do it in a way in which I am possibly content. So I suspect I'll be holding on to it indefinitely. Personally the workwear thing doesn't appeal, although heavy ivy/70s campus style is ok when I am unable or unwilling to dress up. The only other style I am really tempted by is what I see on those mid 50s to early 60s continental movies. If I had the money to go to an Italian or French tailor to get a late 50s style 3 button suit or jacket I would be tempted, but I'm sure even then I would mix it with vintage Brooks shirt and gunboats.

Still ivy is not for everyone. For all the faux ivy that is or has been on trend in recent years, the real deal is increasingly unfashionable, so I can understand people wanting to move with the times.

However I'm an aesthete, and as far as I'm concerned every time I wear an old Makers BD I become a walking art gallery, regardless of whether or not the rest of the population notices or shares the sentiment. For that reason I can't imagine myself letting go of the natural shoulder.

A maverick opinion perhaps, but I sometimes like the English Jermyn Street style shirt as an option to the button down with a natural shouldered jacket or suit.
It was worn back in the Ivy day in America sometimes.
Personal choice should override other people's rules of proscribed dress?

Hard to say what a Jermyn Street style shirt is now. There are a multitude of collar types on offer down thereand several places do button downs, just not very good ones.

Astaire was more like ivy with an English twist imo. I sure as hell haven't seen any Brits in the 50s looking like that, but aside from a few details he had a common US 50s look.

Well I don't think any Brits were looking like that in the 60s either. I agree though that he definitely had a uniquely English-influenced take on the look. He was also an expert at combining clothes (or maybe he just looked good in any combination of colours).

Mr Astaire favoured Anderson and Shepard for his tailoring.
G. Bruce Boyer's book 'Fred Astaire Style' is a good read, although interestingly he tries to connect his style with the pre-war US collegiate style ( and fails IMHO, Fred's look is too eclectic to pin down to one influence).

Most of my evidence is in the book,
Constance Valis Hill - Tap Dancing America: A Cultural History

I was researching a 'one-legged' tap-dancer Clayton 'peg-leg' Bates and came across the 'neck tie as belt' gimmick , which FA 'borrowed' later.
Further digging has pictures of dancers ( both black and white ) in what is pretty much the FA look in the early '20's it seems the deeply pleated 'no break' flannels gave great freedom and accentuated the leg and foot movements of the dancers on stage.
The 'nipped in' shorter jacket I've assumed was for much the same reason.

Another book worth looking at is
Jim Siegelman - The Book of Tap: Recovering America's Long Lost Dance
Gives an interesting overview of the change in performers attire ( mainly covers what the author describes as the 'post Gene Kelly years but also has some great info on the early C20 but few pictures).