Somehow this morning I got to reading in more detail about what the Cynical Network plugin does.
This is the relatively deep end for me, but after starting to read the docs, I immediately wondered if this was a way to get around the problem of IFTTT not being able to do digest authentication, so there's no way to have IFTTT talk to Indigo directly.
Right now I'm using the Better Email plugin as a kludge, where my damn old SmartThings talks to IFTTT, which sends a Gmail to an account that Better Email monitors. Much less than ideal!
But the IFTTT Maker channel allows it to make web requests, and I'm sure I can specify the port. So, could I in theory configure a Cynical Network TCPin device to listen for a web request and change a variable/trigger something in Indigo?