Reader macro preparation

Since I want to add CL like reader macro to Sagittarius, I have been thinking how. I think I had a solution for it so I'm going to memorise it.
Since R7RS draft has been released 4 times and it has different reader macro for bytevector (blob in R7RS or also bytevector?), I need to switch readers between R6RS and R7RS. By default, it can be both, but if user (for now only me...) explicitly specified the mode with shabang #!r6rs or #!r7rs, it should enable or disable some R6RS or R7RS specific reader macro. Well, it is actually easy to just switch with current solution (currently I just see the flag of it and check). But it's not so smart when R8RS or R9RS appears.
So, I'm thinking to add reader macro sets to VM and for future even libraries. The concept is really simple, I just need predefine reader macros for R6RS and R7RS it can be shared its implementations and when #!r6rs or #!r7rs appears switch the set. For this purpose, this behaviour must be per file like current shabang and by default it should have everything (just my preference)
How to do it? The point will be 2 or more letters reader macro such as #vu8(...) or #u8(...). I am thinking I will add 2 sets to VM. One is one letter reader macro and other one is 2 letters reader macro and 2 letters are high priority (or else bytevectors will be invalid vector syntax ...)
Well, I wrote about reader macro however first of all I need to finish replacing regular expression library...