This is a list of the SRFIs in final state that extend the R5RS lexical syntax.
SRFI 4 provides lexical syntax for homogeneous numerical vectors of the form #u8 list, #s8 list, #f32 list, etc.. PLT, Gauche, Gambit, Chicken, Bigloo, Guile, Kawa, Scheme48, STklos, RScheme provide this SRFI. A close variant of this syntax, #vu8 for unsigned byte vectors is provided in R6RS, which means that IronScheme, Ikarus, Larceny/R6RS, Ypsilon, and Mosh also support it.
SRFI 10 provides #,(keyword . args), which causes a procedure bound to keyword to be applied to args at read time. This is similar to, but not the same as, CL #, syntax. Gauche, Chicken, Guile, SISC, STklos, RScheme support this SRFI.
SRFI 30 provides #|...|# nested comments. PLT, Gauche, MIT, Chicken, scsh, Kawa, SISC, Larceny/R5RS, STklos, RScheme, Scheme 7 support this SRFI. It is also part of R6RS, which means that IronScheme, Ikarus, Larceny/R6RS, Ypsilon, and Mosh also support it.
SRFI 49 provides indentation-sensitive syntax. There is no known support for this anywhere except in the SRFI itself, which is written in Guile.
SRFI 58 provides CL-compatible #nA datum for multi-dimensional general arrays. This SRFI is supported only in SCM, though Chicken provides a non-SRFI egg that supports the same syntax.
SRFI 62 provides #; to comment out a single datum. PLT, Gauche, MIT, Chicken, Kawa, SISC, Chibi, Larceny/R5RS, and Chibi support it. It is also part of R6RS, which means that IronScheme, Ikarus, Larceny/R6RS, Ypsilon, and Mosh also support it.
SRFI 88 provides self-evaluating keywords, similar to those in CL but with trailing colons. This is DSSSL-compatible. Chicken, Guile, Kawa, STklos, Scheme 7 support this SRFI.