LSUBR CONS and back-quote

[RWK at MIT-MC (Robert W. Kerns)]

I think the best reason for wanting LSUBR CONS is so that the code
that you write with backquote is somewhat readable...however I would
disagree that "`" is generally useful only for macros.  I often find
I want to generate list structure that shares many of the characteristics
of EXPR code, but is not code at all.  For example, it is the most convenient
way of consing up MACSYMA expressions, say to represent the sum of expressions
A and B, one would write `((MPLUS SIMP) ,A ,B).  I think that this
kind of application is very common, and would like to see backquote in
the standard readtable.