(With apologies if this has previously been expressed -- I've been tied up with tasks for a week and am behind on my reading.)
With long experience with MARC, my primary concern with BibFrame is that it replicates the existing division in the MARC-iverse between bibliographic, authority, and holdings records. If BibFrame (or whatever turns out as the replacement for MARC) is going to adequately serve a data-verse framed on FRBR modeling and RDA relationships, it needs to be developed along lines that afford greater parity and agnosticism between the various FRBR entities. It is not sufficient to merely recreate MARC's silos with the ability to provide linkages thrown in. A more powerful arrangement needs to be developed, in which the existing MARC structures need to be relegated to a carefully constrained subset of the new system.
As a holder of a B.S. in Mathematics, I cannot help but feel we are at a point analogous to the transitions in the understanding of numbers -- from roots in counting by whole numbers through a whole sequence of transitions to complex numbers. Each of these transitions were preceded by periods where certain questions couldn't be answered (what does it mean to count nothing? what does it mean to take 3 away from 2? what is the square root of of a number that isn't a square? what is the square root of a negative number?). Each expansion of the concept of number has been accompanied by a corresponding expansion in the ability to solve questions and the power to apply those solutions. We have seen similar transitions in our field in the transitions from dictionary catalogs to card catalogs, and from strictly card-based cataloging to the MARC surrogates for catalog cards. The next evolutionary step awaits us. It will not be fostered by preserving the constraints of tripartite data file construction.