There's a very simple way to simply SSH to a BTMM/iCloud computer:
In Terminal, in the Shell menu select New Remote Connection... (cmd+shift+K). From here you can browse by ssh/sftp/ftp/telnet hosts on the local or BTMM network.
This is obviously much easier for the individual apps that support iCloud/BTMM lookup (e.g. you'll also see file shares in the side-bar of Finder, and remote Airport devices in Airport Utility), but I'll leave the full instructions below for the more arbitrary use-cases.
It's no longer done via
@computername.mobilemename.members.mac.com, it's now done via
members.btmm.icloud.com, and its no longer as simple as your
Step 1: Find out your iCloud BTMM domain
Either of these commands will provide your BTMM domain:
# dns-sd -E
# mDNS -E
The output is formatted slightly differently, but what you're after is the numeric ID, it'll be something like
Step 2: List Computers
You can use these tools to browse that domain for services, e.g. for ssh servers:
# dns-sd -B _ssh 12345678.members.btmm.icloud.com
Or if you already know the hostname just access it directly as
computer-name.12345678.members.btmm.icloud.com. (Any spaces in your computer name will be hyphens in this domain).
You can only access this from a computer that is also set up for BTMM on the same account, because this hostname will resolve to an IPv6 address that is really the end of an encrypted network tunnel between your BTMM computers.
If you want to see the IPv6 address for a specific host, you can type
# dns-sd -G v6 computer-name.12345678.members.btmm.icloud.com
And it'll output something like:
17:37:47.504 Add 2 0 computer-name.12345678.members.btmm.icloud.com. FD11:993E:64AE:4DEA:011F:FBD1:F444:11A1%<0> 152
Step 3: Connect
# ssh firstname.lastname@example.org
I'm not sure if that number will ever change, so you may or may not need to repeat Step 1 at some point later on...