Advanced features of xkeyval for LaTeX3

Currently, LaTeX3 only provides parsing of key–value input into separated keys and values. I’ve written the keys3 package as a possible implementation of keyval for LaTeX3: this is based on pgfkeys from the pgf system. However, there are some features of the xkeyval package that I’ve not yet covered. In particular, I’m wondering about the ‘preset’ keys system (\presetkeys and relatives) and the ‘pointer’ system (\savekeys and so on). I’ve not really used these, so I’m not sure what might be needed for LaTeX3.

I think that LaTeX3 needs to have built-in keyval support which can cover everything that can be done by add-ons in LaTeX2e. I’d appreciate ideas on what needs to be added to keys3 to achieve this.