Tableless Design
One of things I would love is to be able to ditch the three column layout and move to modern tableless design practices. (Actually tableless design via elegant css is many years old now, so it's not that new.)
It is possible to do tableless desing with oscommerce and the sts contribution but it ain't easy. You basically have to recode all the php boxes.
Tabless desgin has many adavantages: less code therefore better performance, more search engine friendly, once you get the hang of it it is far easier than messing around with tables, much easier to change designs and layouts, plus lots of other benefits.
Anyway, do that and that would be something.