Read these:
http://www.fsf.org.uk/news/news0018-safestanding.html
http://observer.guardian.co.uk/safestanding/0,8221,441632,00.html
I've looked into it before but have forgot most of what I learned after spending time researching it, I can tell you for certain that the club would have no problem introducing it other than it being unlawful and also not wanting another save our seats but that wouldn't be a problem if they expand the ground.