any small chance ?
Demoscener would love it. I would love it 
what does that mean?
Grab your programming developer environment and start coding i should say…
Xrns is an open file format and you can study the whole behavior of Renoise it’s command processing with the demo. Everything to make a basic player possible is already present.
Uhm, no. guessing from the outside sucks and rarely gives complete results. And with every revision of Renoise the guessing starts again? Checking everything to see what changed? That is already a waste of time, and furthermore: it’s not just command processing, it’s also the internal fx.
Coding “kinda similar ones” won’t cut it… a “basic player” is no player. If it just supports the simple stuff you’re much, much better off with the good old tracker formats and all the labour that went into correct replay routines. Seriously: if you strip the internal fx and VST, Renoise has less features than FT2 or IT2 (not sure if that is true, but you get the idea).
What is proposed here is stripping Renoise the app into Renoise the library - no GUI etc, and an API to load and start/stop songs. I don’t know if that is feasible or likely, I rather doubt it, but answering that XRNS is an “open format” is kinda silly IMHO.
Now that’s the best point of your story:a developer is much better off with the old tracker formats and they probably also think that way since adding fx routines costs more cpu consumption and in some cases even causes delays, trust me a Renoise engine cuts cpu cycles that is rather spend on graphic calculation routines.
If you would include VST support, the list of worries gets larger:
Simply because one who wants to use the player inside a demo, then also needs to supply any of the involved VST plugins.
Regarding Free plugins this is not the biggest disaster, but other things you walk up against (besides not being able to include commercial plugins) are:
-copyright limitations (vst plugins may not be included with the work of the artist even if the plugin is free)
-(older version) vst plugins no longer available for download when plugins are not included.
-system limitations (not being able to let the vst perform decently)
Lots of players have been made without the knowledge of how the internal worked.
Ofcourse this also has lead to players doing lots of wrong stuff because it did not incorporated the behavior of situations where different command combinations were used to achieve a specific effect.
I for one knows this best because i have made so much stuff where XM or IT2 players deserted me on moments that i could not use it → I understand some of this pain in this aspect too well.
But for various formats players were developed by coders who did not got a ready-made engine by the developers of the music application. And existing mod-player libraries were also written by programmers who did not wrote any of the music applications that their player library supported.
XRNS reveals a lot more than RNS did because that was closed, in that sense any developer is able to write a basic player, the rest is trail and error by testing songs.
There is at least something to work with. You can call it silly, it has been done quite a while so far… so does that mean that coders became lazy in finding a challenge to write a player?
If no one wants to take this challenge i think in that manner then the Demo scene either is not interested in using such a player, or the demo scene is pretty much dead.
For sure the last case does not compute here, but as i already stated :coders who want music in their demo, rather use a simple Mp3 decoder which suffices, simply because the music engine is nothing to impress anyone with on the big screen.
If there really was a need to use a Renoise engine, i would have expected there would already be an existing library that more or less did its job on this. (No matter if that was a half-assed implementation or anything near a reasonable level).
If you have to ask the music application developer for an engine, that means that there is lack of interest in the coding world so if that engine would be released, it would not be used anyway.
IMHO, waste of development time.
Dude, just think about it as “music app X as a plugin” (which is not quite the same, because it also includes GUI stuff). Yes, it that requires work on part of the developers… but much, MUCH less work than to “recreate it from the outside”. Yeah, it’s more than a bunch of #ifdef’s - but whatever work it takes, ONCE that compile path is set up every update of Renoise would automagically spit out a player .dll. At least in theory. Get it now?
That is because there is no point in it without the Renoise FX. And nobody from the outside can do that. The interest on part of the outside can only expressed by asking.
Exactly. So why invent the wheel twice, when Renoise does this already so superbly?
That is a question for me as well (regarding the internal DSP fx and instrument Fx that is then…), only Taktik can answer if he got questions about the Fx handling.
This might be a nice “gimmick” for the often-talked about “commercial license” 
Well, try to decide if I should do this, or spend time on all the other wishes you have for Renoise. Of course this might be useful to someone, but is this important? Renoise songs in Demos? Forget that, Renoise is no lightweight module player. Playing Renoise songs in your own built applications? Then use ReWire…
That’s why I said “I don’t know if it’s feasible or likely”… 