Livestreaming revolves around sending users media in segments, and the size of those is everything. Large segments introduce a lot of lag, since it takes longer to process them, but short segments can be wildly inefficient. The BBC's methods either shrink a given segment or create segments in a progressive format that can be sent down the pipeline the moment they're ready. This wouldn't completely eliminate the delay, but it might help you avoid spoilers.

You're not likely to see this method in use any time soon, since it would involve coordination with the industry at large to make it a standard. To an extent, it's also addressing an issue that has already been solved in certain cases. Microsoft's Mixer livestreaming service, for instance, has a near-zero latency feature. However, this does promise a day when you can safely watch a sports championship or season finale without dreading reactions around the neighborhood.