I think parsing [http://www.someurl.com] as <a href="http://www.someurl.com">[1]</a> is very useful for documenting sources within articles, particularly quotes from web-accessible material. See the breastfeeding article, for example.
But you can still do that with [http://... (1)] (or [http://...%7C(1)] -- I plan to allow the use of "|" to be consistent with internal link syntax).
Would it be possible to have [http://www.someurl.com description] expanded in the printable version?
That's certainly doable, but I think I'll just make the conversion do this:
[http://...] ==> [http://...%7C(1)] http://... ==> [http://...]
And since the latter will print the URL, the functionality won't change much.