I have two suggestions for future developments:
1) In my opinion, you could add a nonlinear element that accounts for a pinched force - deformation relationship. I would imagine it being something like the Pinching4 material that OpenSees has: http://peer.berkeley.edu/publications/peer_reports/reports_2003/0310.pdf
2) you could add some sort of graphical representation of development of plastic hinges, or damage/limit states.
Keep up the good work!