To me the file in the GIG format met.
In OpenMPT in the bookmark Instruments chose loading "*. *" ;)
What my surprise when OpenMPT opened this instrument was!!!
The file contained multilayered instruments. Only the last were loaded in the samples list. Samples were placed incorrectly concerning notes... :( But range was full and nothing superfluous!!!
It was necessary only to paint samples on notes and to expose Envelope.
Did not meet a mention of support of this format in OpenMPT anywhere.
There were two questions:
1) Whether it is planned to support this format in the future?
2) I'm it was not necessary to use GIG files before. Do they have an advantage before SF2? Whether there is in general a sense of support of this format?
It's not planned, no. From a quick look it seems to be yet another complex soundfont format similar to SF2 so OpenMPT would most likely only be able to support small portions of the entire format.
If you have any GIG files, it's probably better to convert them to something more modern like SFZ, I suppose Awave or Extreme Sample Converter could do the job.