> I would rather use Ext4 everywhere for everything. Is the problem preventing wide adoption of Ext4 GPL?
The BSDs don't support ext{2,3,4} particularly well, and Linux doesn't support FFS/UFS particularly well. I mean, there's support for these things, but it's far from complete or perfect and it's taken a long time.
It's just a fair amount of effort to implement filesystems well, and there's very little tolerance for errors. Ext4 isn't spectacularly complicated, but it's not exactly a simple FS either. I think that has more to do with lack of support than anything else: lots of effort for not all that much practical benefit.
And ext has plenty of documentation and they haven't implemented that either.
So I think keeping down the software complexity is the more likely method. Down to
1. The limited software investment these companies make (often just buying and reskinning firmware from AMI)
2. The limited space available on the ROMs due to hardware cost savings (e.g. companies have had to drop GUIs or support for less popular APUs to add support for new generations of mainstream CPU in firmware updates)
Although very complex and very undocumented, NTFS has actually been adopted very widely and quite reliably. Most of the pre-smart TVs and set-top-boxes can read FAT and NTFS USB drives which makes NTFS the only choice if you want movies exceeding 4 GiBs.
ExFAT can support those. You could also use the UDF file system.