This page is part of the web mail archives of SRFI 76 from before July 7th, 2015. The new archives for SRFI 76 contain all messages, not just those from before July 7th, 2015.
I too agree with the pragmatic problems with the opacity that have been presented. Although I do think that there can be good reasons for needing security, the oversimplified opacity flag is no actual provision for security. If anything is to be provided to this effect, it would make no sense to have anything less than general capability security, and I doubt whether anyone feels this would fall under the scope of this SRFI. Also, are sealed records at all useful in a single-inheritance system? Are there any compiler optimizations permitted by them that would be impossible otherwise? I can't find any rationale in the document.