I don't know if anyone is checking Starmen.net here sometimes... but a person there had a few Blue Disks with proclaimed Mother 3 data on it.

Now, when he started the disks 2 of them did contain data. Not Mother 3 as everyone hoped, but it has some other interesting stuff on it.
To quote his findings:

"I finally had a chance to try the disks yesterday.

The first disk didn't boot. It tried to load it and then stopped.

The second disk booted properly. But it wasn't Mother 3. It was Sim City 64.

The third disk didn't boot.

The fourth disk booted properly. But it wasn't Mother 3. It was Mario Artist.

It was exciting and dissappointing at the same time. They aren't blank. Which was nice. But I was really hoping for Mother 3. The way the disks are labelled makes no sense. But I noticed that they once had paper labels on the back. That probably had the game name on them.

All four disks contain content.

They were last modified in 1999. "

And another interesting quote followed from someone in that same thread:
"you said they were last modified 1999 right? Sim City 64 was released February 28, 2000. "

Beta stuff maybe? I doubt it, but it's still interesting.

It would be interesting for hackers to have access to dumps of those 2 non-booting disks and see what is on them.

Since they are dev stuff maybe the don't boot by themselves, maybe they need a cartridge that has the boot program and the disks only contain data to be used by that cart program.

They are empty, possibly.

that would be kind of sad