I have not touched PS3MediaServer for a while, but let me give you my comments anyhow. Be aware that I might be wrong, though. Things have surely moved on since I last had a look at the code.
1) AVS files
As far as I know, AVS are AVISynth files, that is, script files for non linear video editing. The only solution I see is if PMS does transcoding on the fly. I suppose that AVISynth could feed that decoded stream into mencoder without much hassle ( http://avisynth.org/mediawiki/FAQ_frameserving
). I did not have a look at how PS3MediaServer works with media files, so I cannot tell you how difficult this task is. Anyhow, AVISynth only works in Windows, as far as I can see from their website.
2) Simple Active/Inactive Event CMDline interface - plugin
As you said, somebody created a "shutdown" plugin some time ago, where a single command was executed (was that really me?). The thing about plugins is when they are executed. It looks like the most promising one for you is StartStopListener.https://github.com/ps3mediaserver/ps3me ... tener.java
What this prototype shows is that some code can be run when the server starts serving a file and when it stops serving that file. It still does not say anything about media server doing grunt work (so it will not play well with more than one client if you are not aware of them), but this one is worth looking at. The biggest worry I have is that some media renderers might stop if these functions take too much time.
Other types of plugins can be found at:https://github.com/ps3mediaserver/ps3me ... s/external
3) General CMDline interface - plugin
I am against anything that involves typing on a TV remote (by the time you finish typing, you could have gone to the computer and do whatever you wanted). As you do not want that, I can see how the "shutdown" command could be easily expanded with a configuration window inside PMS.
If I look into the details of your request, I can see that coding (2) and (3) should not be too much trouble, at least compared to (1). Writting plugins is just a matter of class inheritance, typical of any Object Oriented Program like Java. Learning Java isn't complex either. However, I wonder how easy is it to create the plugins nowadays, as you might need to download the complete source code.
The biggest trouble you can face with (2) and (3) is user privileges. As far as I know, you need to be an admin in order to start and stop services in both Windows and GNU/Linux (I have not much experience with MacOsX). UAC in Windows might require physical access to your computer. But that is probably one discussion that is not really focused on PMS.
You also ask if I can see any benefit on implementing these. Well, I have been working without AVISynth for some time now. And at that time, it was used for DVD encoding tasks only. As for the extra commands, when I am in my couch, the last thing I want to do is to run any extra batch program in my computer. My media files are in such a format that my UPNP-AV server does not need to transcode anything for my "smart" TV, so I do not see any need to fine-tune my computer to be more efficient. TSMuxer has been a better friend than transcoding, and that does not need a lot of power.
As I have said at the beginning, I am not working in PMS at all. I do not even have PMS installed in my computer anymore. Java is not too hard to work with. However, the biggest risk I see is in installing Eclipse (or whatever JavaIDE you want), download PMS and compile it. And I say risk because there are so many options and so many new things that you might step out.