When we went to Ready! API, I had been hoping that the assertion editors would get a re-working. However, they still have all of the same short-comings of SoapUI.
Specifically, the editors don't give you very much realestate in their default size when you open them. I always have to drag the editors to give myself more space to work in.
To address this, I suggest two improvements:
Add a Maximize button on all editor windows that are currently resizalbe (e.g. XPath and XQuery editors, etc.).
Have each type of resizable assertion editor remember the last size that it was openned to, so that whenever you open an assertion editor of the same type, it'll open at that size. This should be persistent between sessions, and be by assertion type (NOT specific to individual assertions--far too many of those to keep track of).
Here you can review submitted feature requests and vote up the ones you like! If you can't find the feature you want - go ahead and suggest your own idea. Ideas with the highest rating can be implemented in the product.