I was wondering if the GOG version of S2 will be updated so it would be possible to upload S2 save files for future import into S3, as the current Steam version allows. I guess if the S2 saves are in the filesystem it won't be a problem, but the possibility of a cloud save would be nice.

I hope this happens soon as well.

As it is I had to copy the saves to my phone, use the Android version of Season 2 to upload the saves to Telltale, and download my choices into the GoG version of Season 3 that way.

I created a support ticket with Telltale, and they replied me with the following:
"Thank you for providing this information. We have now seen this issue in the studio and are investigating further. We submitted an update to add the "Upload" button in the GOG version, but this has not been added.

Unfortunately, I do not have a specific time frame for a potential resolution for this issue. If you would like to play A New Frontier the moment you acquire it, I recommend recreating your backstory through our Story Generator".

Since I didn't remember what choices I made in S2 (it's been a few years), I had to import the from the filesystem, so thanks SANAFABICH, that was a useful advice.