I'd make a case for life of artist +n (10 or 20 sounds reasonable) years or, say 30 years whichever is longer.
edited to add...
Of course that works for individuals but not for companies - forget that proposal then, makes no sense in that context.
Corporate-owned copyright at the moment is still linked to the lifetime of the specific people who created the work in question. If we take films as an example, the copy which makes them will invariably own the copyright, but the duration of it is the life of the last "author" to died, plus seventy years. "Authors" of a film are:
(a) The writer/s of any original work the script is based on
(b) The writer/s of the script
(c) The director/s
(d) The composer/s of original music specifically writtent for the film
We can take the example of the 1936 film
Things to Come, with the script being written by H.G. Wells (d. 1946), based on one of his own books, so that covers (a) and (b). It was directed by William Cameron Menzies (d. 1957), but the original music was by Sir Arthus Bliss (d. 1975). This means the copyright lapses after the end of 2045, but it is currently still owned by ITV Global as the successor company to the studio (London Films).
Generally, where a work has no known author, the 70 year copyright clock starts ticking from the date of publication or otherwise being made available to the public. Under this rule the copyright on the production photographs taken during the making of
Things to Come - because nobody knows who the on-set photographers were - would have expired at the end of 2006, although because they were subject to an earlier rule of
creation + 50 years, it was actually the end of 1986.