Thank you all for the feedback, this is very helpful. Let me share with you some more of my thoughts.

I wanted to get a better understanding of which features in GoatTracker would be most essential and which features are rarely used. I was curious how typical SNG files look like and see what's typical and what effects are less common. So I wrote a tool 

to convert SID files back to SNG. Having looked at a few files, I think I have a better idea now.

Case in point is the song order list which allows for lots of flexibility like repeating patterns and transposition, all independent for each channel. That is useful if you care a lot for space efficiency but I would like to forego this and instead just have a simple table not unlike how Fakesid currently does it. As it turns out, all the files I looked at have a very regular structure where simultaneously playing patterns always have the same length. That's perfect.

So, I do not want to support everything that GoatTracker can do, for example all the song order list stuff or the channel tempo command. That's why some SNG files will cause issues when importing but in such a case I should be able to print out a warning/error describing the issue. 

usage: sid2sng [options...] sid-file [sng-file]
 -nopulse
 -nofilter
 -noinstrvib
 -fixedparams
 -nowavedelay

for file in *.sid; do ./sid2sng "$file" "${file%.sid}.sng"; done