Pro Very mature
Ext4 is now officially old enough to purchase and consume alcohol in the United States, having first been released in December 2000 as part of Linux kernel 2.6.28. Its status as the "primus inter pares" (first among equals) of in-tree Linux file system drivers ensures it continues to see a steady stream of upgrades and enhancements as well as bug fixes with no plans to be replaced by a new major release of ext or deprecated in favor of another filesystem entirely. It almost certainly will be with us for another decade or more as the default Linux filesystem.
Pro 48-bit block addressing
The upgrade to 48-bit addresses took the limitations of the filesystem from a tight orbit out into deep space, with the maximum volume size now a comfortable 1 EiB (that's exbibytes with an 'e', over a million tebibytes) and the maximum single file to 16 TiB when using the default 4KiB block size.