A lot of the 10-bit H.264 videos out there are smaller than they would be if the same people had released them with 8-bit encoding. At some point, the quality difference between the encoded version and the source video becomes negligible, so it's natural to expect that better compression would result in smaller file sizes for any given raw source.
The time when this doesn't apply is when you're currently losing a noticeable about of video quality to keep file sizes down. Say that you're a movie streaming service, and you want to stream a fairly new movie. You have it at very high resolution, but if you wanted to stream it at Blu-Ray quality, that would really eat up your bandwidth, so you decrease the file size to something you're comfortable with, and get as much quality as you can within those limits. Better compression, in that case, would mean either better quality at the same file size, or bandwidth savings at the same quality, or some combination of the two.
So: I would expect this to make pirated TV rips smaller, pirated Blu-Ray rips larger or smaller (depending on what the encoding is optimized for), and streaming video either higher quality or smaller, depending on your connection speed and how much bandwidth they're willing to pay for.
The time when this doesn't apply is when you're currently losing a noticeable about of video quality to keep file sizes down. Say that you're a movie streaming service, and you want to stream a fairly new movie. You have it at very high resolution, but if you wanted to stream it at Blu-Ray quality, that would really eat up your bandwidth, so you decrease the file size to something you're comfortable with, and get as much quality as you can within those limits. Better compression, in that case, would mean either better quality at the same file size, or bandwidth savings at the same quality, or some combination of the two.
So: I would expect this to make pirated TV rips smaller, pirated Blu-Ray rips larger or smaller (depending on what the encoding is optimized for), and streaming video either higher quality or smaller, depending on your connection speed and how much bandwidth they're willing to pay for.