Steven Weinberg has lately been critical of QM. He now also has a technical paper out called 'Lindblad Decoherence in Atomic Clocks', available on arxiv. Here is the abstract:

It's a short paper (6 pgs of text), arguing for objective collapse (a la GRW/Diosi-Penrose/etc) instead of Copenhagen/MWI. Based on Ramsey-method atomic clocks frequency measurements, Weinberg gives upper limits (based on Ramsey transition times) for objective collapse below which the scheme is already ruled out experimentally. He also proposes two different ways in which objective collapse can be sought out further in future atomic clock experiments.

This passage in particular (describing one of the two ways forward experimentally) seems very interesting. It is somewhat reminiscent of the Marshall et al. proposal of putting a tiny mirror in superposition in order to detect or rule out the Diosi-Penrose objective reduction scheme.

From what I last heard from Penrose (past November), Dirk Bouwmeester is currently still hard at work on this experiment and we will have an answer within a decade.

Here is a somewhat recent review of the theory and experiment of decoherence, both environmental and intrinsic, concomitantly offering a Feynman path integral approach:

Of particular interest for the current thread, in light of the Lindblad equation, are the following passages, especially the highlighted part:

It doesn't seem Weinberg has taken this into account either...

NB: Reference 1 and 14 are two works by Feynman from during the 60s:
[1] Feynman, R. P., & Vernon, F. L. (1963). The theory of a general quantum system interacting with a linear dissipative system. Annals of physics,24, 118-173.
[14] Feynman, R. P., & Hibbs, A. R. (1965).Quantum mechanics and path integrals [by] RP Feynman [and] AR Hibbs. McGraw-Hill.