[The following uses the "BIBFRAME Authority" name, but we really do need a better term for these. Maybe "inclusive links" or "capture/cache connectors" would work, to convey the idea that the BIBFRAME authority is a linking structure that can capture information from an external source and include it, manually or algorithmically, in the indexable, displayable description of a BIBFRAME Work or Instance. Anyway, that's how I'm understanding BIBFRAME Authorities now.]
If BIBFRAME Authorities are able to carry the weight of added access and description for a given BIBFRAME Work or Instance, that opens up an interesting set of possibilities. Traditional authorities will be sources of alternate names and presumably other information which can be captured and cached on the BF Authority for local context indexing and display in relation to one or many BIBFRAME Works and Instances.
Will it be possible to use a BIBFRAME authority to link a BIBFRAME Work describing a FRBR Work to a BIBFRAME Work description of a FRBR Expression? Something similar could be done if traditional uniform title authorities were remodeled to include the full range of FRBR Work attributes and components, but that would be up to other agents, not BIBFRAME. Personally, I'd be happy to see BIBFRAME include a model for a generalized set of elements and relationships true for the FRBR Work as a type of BIBFRAME Work. The goal would be to capture and cache those bits of access and description specific to the FRBR Work and include them as data for all the BIBFRAME Works describing Expressions of the FRBR Work through the use of BIBFRAME Authorities. This should be a close parallel to using BIBFRAME Authorities to capture and cache for local use bits of information about named entities which reside in traditional authorities.
"Stand alone" is a complex concept in webbed environment. Can we say that a description "stands alone" if a comparable static description can be harvested from the webbed description including the things it links to (e.g., BIBFRAME Authorities)? If so, and if the link to BIBFRAME/FRBR Work descriptions can be included as targets of the BIBFRAME Authority relationship rather than as simple related record links, then I think we could have the division of descriptive labor which FRBR envisioned without sacrificing the ability to assemble and communicate "stand alone" descriptions of Expressions/Manifestations or Works/Instances, or requiring a major reconceptualization of BIBFRAME, or requiring an overhaul of MARC its twilight years.