So I really love the concept behind xlights, its so simple, yet so powerful.
How about if xLights could play two sequences (of the same song) at the same time? You would load up sequence 1 and sequence 2 ... and you could play these back using xlights as a single song/sequence ... and still map out the various channels for each to the desired networks/protocols as you can today ... but somehow use 'the song' (music, start of audio waveform) as the unifying sync element between them.
The idea is that you could leverage your work from one year to another in a very easy way ... just add on stuff in a sequencing program and export to a format the xlights can play (like LOR or VIXEN).
Even though (the argument can be made that) you can convert say from LOR to LSP and then back again ... you loose significant things every time you convert. And you don't get back a sequence that is really the same when its all said and done.
Just an idea.