All retailers (whether train operator or third party) have access to the same information regarding scheduled train times, rescheduled train times, and disruption information, via the same few data feeds (namely the DTD feed and the Darwin feed) that would enable the things that Hadders and I are suggesting are done, to be done. I don't think the development cost need be huge, although handling the many edge cases (especially where TOCs / Network Rail are used to continually changing data right up to departure because it doesn't currently matter) is a challenge.