I do not like the "next fastest train" stuff. I have noticed trains will disappear from that when they still haven't departed (presumably they think there is not enough time to get to the platform); much prefer the traditional destination screens which are clearer for me at least.
A lot of the time now I use my phone. Indeed at King's Cross the platform number showed on my phone before it came up on the station screens (and of course there are ways of finding out the booked platform well before the train leaves). They like cutting it fine there for some reason, I could well imagine people missing their departure if they were not paying hawk like attention.
I would be putting
www.traintimes.org.uk/live/rdg/tap into my browser and ignoring the screens at Reading!
I used King's Cross on Monday and my train showed the platform 20 minutes before departure time. I find Paddington much worse, the Bristol trains often don't show the platform until less than 10 minutes before departure time, which if you have a bike booked, and have to get to the farthest end past a lot of other passengers all making their way through the barriers and then down the narrow platform, is definitely not enough time. I returned from Paddington yesterday and the platform appeared on the screen just under 8 minutes before departure time. Fortunately it wasn't too busy (middle of day) but I still only got on with about a minute or two to spare.