Diego, it’s possible to get full 3D during boot up. It would require copying bits of mesa into initramfs and would require restructuring how plymouth works a bit.

Having said that, boot is something that’s not supposed to take a long time. In an ideal world we’d go from bios to instantly logged in. We can’t acheive that, yet, though, so plymouth is a way to add a little bit of polish during the waiting period. It’s not something the user should really “notice” so much as an independent part of the system, but instead it should just be part of turning the system on.

That’s why I’m a proponent of keeping things simple.

Also, note there is a cost to doing fancy things. Every megabyte you add to the initramfs is another megabyte that has to be decompressed before the computer starts booting and kept in memory while the machine is booting. Every animation and effect a splash renders uses machine resources.

You don’t want to end up in a situation where the boot splash significantly slows down boot up. That would be missing the mark, I think (and is a problem Fedora had with rhgb before plymouth).