A few things - this is one step in a long, LONG path. AV2 is currently unusable in its current state (the encoder typically runs at around 1fps on good hardware), and likely will remain so til ~2028 when the first av2 hardware accelerated chips start dropping. Even then, I wouldn't expect AV2 streams to be common til 2030.

IMO, if it were just the efficiency gains on the table (which are substantial - ~20-30% over AV1), I'd say that AV2 isn't worth it. The biggest thing it does add though is multi-stream support, which will be a big win for VR and live sports. The other fun thing is you can send an alpha channel as a separate stream, which the file will then composite for proper transparent video support.

Based on AV1's trajectory, hardware encode isn't necessary (though it is nice). The current encoder is a reference encoder. Now that the spec is finalized, expect significant speed improvements from production encoders (realtime likely won't happen until we get it in hardware though)

Where do you see information about the efficiency gains over AV1?

That's fine and not anything new for codecs, they always take a long time before mass adoption.

Take a look at AV1 itself, you can't even say it's really ubiquitous on all hardware. It's quite well along in adoption compared to early days, but some mobile devices are still lacking hardware acceleration for it.