Anyone interested in this topic might want to review the work of
Martin Mallinson, who has been doing apllied engineering in Common
Lisp for many years, and has developed a body of reader and printer
customisations that support friendly engineering notation. He's
spoken about this at ILC --- slides and audio are here:
http://www.international-lisp-conference.org/2005/speakers.html#martin_mallinson
Martin is approachable and I believe he might be willing to share this
code if anyone thought it would be useful in Maxima. Of course,
integrating anything new into Maxima syntax is probably not easy (as
rjf points out) but Martin's experiences might at least be useful to
anyone undertaking something like this.
Engineering math isn't the _best_ math, but it's often the math that
pays the bills.