2016 working paper (pdf and shallow summary) finds that 1984-2014 share of U.S. value added going to undifferentiated capital (required rate of return, based on bond and capital market prices) declined even faster than that of labor, while profits increased from a 2.16% share to 15.70%, explained by increased industry concentration.
Note decline in shares of both labor and generic capital is welfare inefficient (as noted in the paper) and would seem to indicate that profits available to only particularly situated parties (eg through luck, exclusionary networks, political rent seeking) in a way that has changed over last 30 years.
The paper doesn't posit any explanation for increased concentration, but has same findings when excluding one obvious set of industries (involving tradeable goods, thus influenced by increased non-domestic competition) and one set of industries of interest here ('R&D intensive'). Does the latter mean that IP is an unimportant factor in increasing concentration? Or does the non-explanation of increased concentration potentially leave a huge role for IP as it affects most industries, not only R&D intensive ones?
Some previous postings may have hints: