This is a nice thread for necrobuming. I did it in 2016, too.
Of course, you overclassed me with doubling the bump time to 6 years.
Yes, you get an improvement. No it's not speed, especially, more about stability. Originally the Kobo indexing became quite sluggish, when we replaced the original 4GB cards with 64GB and 128GB. So instead of enlarging the partition that was mounted at
/mnt/onboard, we created a very large partition of ext2/4 and mounted it at boot at
/mnt/user. That partitions remained even if the device was factory reset. We browsed them with Koreader.
Nowadays, I think that the original approach from 2013 becomes more reasonable: Just reformat the partition on
/mnt/onboard. Kobo's indexing should have caught up with the larger amount of books. So that's not an issue anymore. And more apps are installed on the onboard partition, which would we quicker on ext2/4.
However, you will get hick-ups. Kobo does thing its own way and you'll have to work around it. So we hacked the
/etc/init.d/rcS boot file to get our way. I haven't looked at the filesystem of Kobo for years. I don't know if Kobo Start Menu (KSM) is still the route to start hacking your Kobo. You'll have to search the threads yourself.
I don't think this is just about reformatting a partition. However, if you like to hack your Kobo. This is definitely one way to get a lot of hands on experience.