While ChromeOS is based on Linux and EXT4 continues to be the most widely used Linux file-system and still is used by default on most Linux distributions, Google developers are dropping support for EXT2/EXT3/EXT4 file-systems from their ChromeOS user-interface.
Among the reasons for Google wanting to rid Chrome of EXT* support is over lack of easily relabeling EXT* volumes from their GUI. When any volume is inserted that has read-write privileges, you should be able to rename the volume in the same way you can rename a file, but EXT doesn't work quite that easily.
What's making the rounds today is this Chromium issue report of "Drop support for ext2/3/4 from Files.app." This issue was originally opened last November but is now generating attention. The file-system support would be dropped from the Chrome OS file manager for EXT2/EXT3/EXT4 file-systems on any external USB/SD storage devices. The fully supported file-systems endorsed by Google would be FAT and NTFS.