Re: One really cool feature...
The ANSI E1.11 - DMX512A standard requires the receiving circuit to be electrically isolated, and has done since 1990. IIRC, only the original 1986 version of the standard didn't require it, but did recommend it.
See sections 4.6, 5.7 and Figure 3. (There may be an RF bypass capacitor to Chassis, but nothing else.)
There is some very old (pre-1990) reputable kit without it, but nothing reputable designed since 1990.
Unfortunately, there are a lot of cheapskate pieces of **** which use an explicitly disallowed receiver circuit which breaks that isolation, either to save ~5p on 5V-ISO and opto or because they have never actually read any of the standard. I'm guessing the latter, as there's been a lot of inaccurate or outright wrong info on the Internet over the years. (Including some app notes with firmware
(PIC) that get it wrong.)
This kind of equipment can usually be identified by the 3-pin XLR connector labelled "DMX", which is also specifically prohibited by the standard.
The standard is currently available for free from PLASA Technical Standards Program.
The reason MIDI uses current loop and DMX512A doesn't is that MIDI is a point-to-point (daisychaining is not recommended, but works for very short runs), while DMX512A is 31-receiver multidrop over very long (500m) runs where the devices could be a long distance from each other.
Current loop doesn't work for a long multidrop run as the resistance of the cable means the current vanishes into the first couple of receivers.