Some folks use proven in both the past participle and adjective alike, while others reserve that form to adjectival use and instead use proved only as the verb. Here’s such a distinction:
- He hadn’t yet proved it.
- Is that a proven fact?
I don’t think that either would raise an eyebrow. Or rather, you could alternately use proven in the first case above, but you could not use proved in the second one. At least, that’s what my ear tells me.
Also, I believe the verdict in Scots law is not proven, not not proved.
As of 2007, the OED3 reports of proven adj.:
This is the usual form in Scottish English (as opposed to proved adj.), and also the preferred form in current North American English. It is now also more frequent than proved adj. in British English.
Its tale under prove v. is much, much longer; I can give only an excerpt here.
Inflections: Past participle proved, proven.
The past participle proven, originally Scots and the usual form in Scottish English, developed from the β forms by analogy with strong verbs like cloven, past participle of cleave v.1, woven, past participle of weave v.1 It is at least as common as proved in current North American English. It is also spreading into other varieties of English, in which the highest proportion of occurrences appears to occur in the past and perfect passive. Compare proven adj., proved adj.
So I really do not think that proven should be considered a deliberate archaism, insofar as in some parts of English it has always had a strong presence, and it seems now to be spreading even to regions where it previously did not hold sway. At least that’s my reading of the OED note above.