On the Scheme Language Steering Committee Nominees page, Will Clinger writes...
The R6RS has given us the option of writing programs in the new and more static language it describes. Two implementations of the dynamic language most recently described by the R5RS have added support for this new mode of execution, and four brand new implementations of R6 Scheme are well under way.That represents a partial success, but this process has disappointed users of the language formerly known as Scheme...
As demonstrated by ERR5RS, the major new features of the R6RS could have been added without forbidding... the dynamic language paradigm of IEEE/R5 Scheme...