Really good ideas in your article...
I like the idea of user stylesheets (smart local stylesheets as you call them), the Opera browser has always allowed for this. Since I use the Opera browser with Proxomitron, I use the Proxomitron to insert a simple stylesheet on all pages (this takes care of link styling and styling of Proxomitron filter replacements). (This is also a trick to use two user stylesheets: one that always applies (prox.css), and one that only is used when necessary (userCss.css).)
A filter which would insert a user stylesheet in Prox is this:
Name = "Insert Prox stylesheet"
Active = TRUE
URL = "$TYPE(htm)"
Limit = 256
Match = "<start>"
Replace = "<!--//--><link href="http://bweb..local.ptron/prox.css" "
"type="text/css" rel="stylesheet" title="Prox CSS" />
In addition to the 'Prox stylesheet', I also use a user stylesheet in Opera (which I can toggle with CTRL+G), to show pages with all formatting removed or altered. It can be downloaded from http://members.outpost10f.com/~jor/files/userCss.css
I've found that using this stylesheet, even the most horrid of pages will display.
And no, Proxomitron is not Open Source, nor free (as in beer) (check out it's unique licencing... ShonenWare
), but it is very well documented, and the author is still making improvements.