I want to be able to make variables based on other variables. Sometimes I want a variable to always be two less than another variable for example. Sometimes I need a lot more than basic math (trig, exponentiation, etc). In general, support for full equations that define variables would be awesome.
Alternatively, linking variables or sketch dimensions to cells in google sheets or Microsoft excel documents (I think google sheets would fit the cloud based model of onshape) would work similarly and allow for awesome things that are available in programs like solidworks but not in onshape.
A text editor would be nice as one of the tabs.
A way to comment on specific sketches/any feature. Maybe in sketches the ability to comment on the actual sketch plane and draw arrows to things, label sketch elements etc would make things much easier to decode if you revisited a complex sketch a long time after doing the first one. Something that looks like the dimension tool but allows you to type and save words would be so so so so awesome for both teaching onshape (explain what everything in the sketch does) and for when working on a document with many other people.