Mechanism to communicate from emulated OS to API

I'm not sure if this is a question or a feature request - if it's a feature and straightforward I'd be happy at giving it a go at coding it too.

I'm trying to find a way for a emulated OS to notify the API of an event or to get information. For example, in DOSEMU you can use the "exitemu.com" to exit the emulator from the emulated OS, and "isemu.com" to return whether it is running in DOSEMU. For v86 I wouldn't want something so specific (since this can run in multiple OSes) but the ability to do something similar, like fire events in the js api or get info, etc.

One way I know of to do this is to use a serial port to send these communications. This works great, but I was wondering if a more "standardized interface" either exists or should exist?

The immediate reason I have for such a mechanism is with running BBS "doors" from node.js, so that after the door program exits (because the user quits the door) it can notify the API so it can clean up and close. For now I'll use the serial mechanism, but a) this uses up one of the serial ports which could be used for a multi-line door game :) and b) I'll have to make up my own comm mechanism for it. No big deal but just wanted to see what you all thought!