I got the device this morning, this is what Nmap says:

    Device type: general purpose
    Running: Apple NetBSD 4.X
    OS details: Apple AirPort Extreme WAP or Time Capsule NAS device (NetBSD 4.99)

I was not aware the Extreme and Time Capsule actually run NetBSD (interesting as well), I assumed they were running the same basic platform the older Express does:

    Running: Wind River VxWorks
    OS details: VxWorks

So there's a change here for sure, it's obvious this new device is more capable but may still be running NetBSD. The Verge ran a story[1] a while back suggesting they were porting Darwin to run on these things for the purpose of replacing NetBsd, which is interesting.

[1] http://www.theverge.com/2012/2/7/2782694/theres-no-secret-pr...