I've just updated the BLOB proposal with a slightly stripped down and simplified version of what was there. I believe this achieves the same goals, meets the most common use cases and requirements, and should not be *too* difficult to implement.
This does not support all he use cases I could come up with (e.g. remote data stores, custom API integration), but we don't have cases were anyone actually wants to do that. Not supporting those allows this proposal to stay fairly simple, but did take those cases in mind and leaves open the opportunity to add enhanced capabilities with additional API changes in the future if needed. Proposal is here: https://cwiki.apache.org/confluence/display/DAFFODIL/Proposal%3A+Binary+Large+Objects
