Linus Torvals has christened it that way, Linux version 5.8 kernel will be the biggest of all time. Incessant work from the developers that will culminate in a massive release after the current 5.7. Therefore, it will be a before and after in the development cycle, and that monstrosity will indicate that it will be loaded with news.
Nothing but two weeks after Linux 5.7Linux 5.8 is being developed with the first RC (Release Candidates) that will arrive to test what will be the final version. According to Linus, it would be almost on par with the Linux 4.9 version, another of the largest in development history by integrating new functions and improvements in all components, subsystems, drivers, documentation, etc.
Linux 4.9 it was huge due to the greybus subsystem that was merged into that version. A project initially designed by Google under the Ara project for mobile devices, but later used beyond that for IoT applications and therefore merged with the kernel.
On the other hand, in Linux 5.8 there is no such signal subsystem, therefore, the size comes by the amount of improvements and developments that there are slopes to add in different areas. In fact, Linux 5.8 received more than 14k commits and some 800k new lines of code, as well as the modification of 14k files.
And 14.000 modified files and 800.000 lines of source code there are many ... Besides, everything is very distributed as I said. The only bigger thing are the drivers or controllers atomisp and habanalabs. But outside of that, nothing compares to greybus.
We'll see how Linux 5.8 finally looks when it launches at the beginning of August, when it is planned (if there are no delays). At the moment, you can try the first rc1 downloading it from here, but just for testing, it is not advisable to use a rc on production machines ... as it is not polished at all and can cause some problems.