Great we're finally getting this. Does anybody know which ones we're missing, i.e. ones that haven't been translated or released in English yet for GOG or Steam?

We are missing:

1. The two Crossbell games (Remastered versions of both of these games are coming out in Japan in April 2020 and May 2020, which increase the chances for an official English translation to be made).

2. Trails of Cold Steel 4 (this has been out in Japan since 2018, but still we have no word on when or if it will ever be translated into English.).

3. The upcoming Trails game which is also coming out in Japan this year, which will be a hybrid of Trails of Cold Steel 5/Crossbell 3/setup for the next sub-series. That definitely ain't coming out in an English version any time soon, and certainly not in 2020.

What are the chances of them re-releasing the 90's games?

IMO those chances are very low. The President of Falcom never discusses the idea of reviving those games when he gives interviews to the English media.

Then again, Falcom does have a habit of remastering/remaking many of their old Ys games. So anything is possible. But I wouldn't expect those 90s games to be coming back.

That's a shame. I'd be interested in playing those.

There are also technically these, but the only one that really counts towards the setting is an online free-to-play game that isn't Gwent, so...