The next Pixie Scheme release (if there is one) will probably be an upgrade to the "R4" ("Revised revised revised revised…) Scheme language standard, involving at least moderate changes in what the built–in procedures are and how they are implemented. The official "R4" report was due out in October, 1990, but as of 1 January 1991, I haven't seen it yet, so I can't say when the next Pixie Scheme release might happen.
Fair warning: The "R4" standard is reported to require that the empty list, (), *NOT* act like the false boolean, #f, when used where a boolean is expected. That is, in R4 Scheme
(if '() 'true 'false) ==> true,
whereas in R3 Scheme — and thus in all releases of Pixie Scheme to date — and in most other Lisps that have ever existed,
(if '() 'true 'false) ==> false.
Much Lisp and Scheme code will break when this change happens. Be warned.
Likely enhancements of my own — not part of whatever R4 may contain — include more file and more I/O procedures, and perhaps a pure functional subset of the language itself.
Wilder dreams include Logo–like turtle graphics, means to evaluate an expression in an environment of the user's choice, and a foreign–function interface.