There are still plans for those home users on 20:1, who do not want to pay an additional £5 to stay on 20:1, to be moved to 50:1 but no timescales are available for this.
It is still unclear if you decide to stay on 20:1 what contention ration PN will put you on. http://www.plus.net/support/adsl/fair_usage_update.shtml item 5 only menations 50:1 products for home. I would hope it's the same as other 20:1 products like teleworker - i.e. you pay for 20:1 so get 20:1.