My understanding is that would be fine so long as the default distributable will run Shen according to the spec. Keep in mind, you can do a LOT of extensions and still run standard Shen. For example, the existing shen-clisp, you can seamlessly call clisp functions by typing them in all caps. I think it would be interesting for someone in this conversation to suggest something that they might want to do to the language that would not allow standard Shen to run also.