I've moaned about it before so nice to be appreciative of London Underground for a change - all tube lines are now represented on the Departure Board page on the TFL website . You can see the arrivals in real time for any train on the system. For the last few years it was restricted to half the lines.
Of course you need an internet enabled device to read this info, so you can't see it when you are actually using the tube or at a station (unless you have a suitable handheld device). But we can perhaps dream of the day when this will be reality, and we won't need announcers to tell us about delays, we will be able to see what is actually running for ourselves and plan our journeys accordingly.