Sadly, I find it very unlikely we'll ever see them around.

My nostalgia lies more with the PS1 and PS2 games, but the problem there is the same: licensed games are very difficult to maintain for an online store. Licenses change hands, expire, before you know there's two or three different companies sharing the rights from whom you need permission. Licensed games are difficult to come around, and it's not unheard of to see them pulled from the catalogue.

In this case the major problem lies with the multimedia rights for Harry Potter lying in the hands of Warner Bros. Back in the day, when they had little to no presence in the gaming market, they licensed the property to EA to make all those games. Since then though they've invested heavily in videogames, buying their own studios to work on their own brands, and becoming a very large publisher in their own right. If you look around for Harry Potter games, the only ones still for sale you'll find are the Lego Harry Potter games published by WB themselves.

In order to see the games here you would have to broker an agreement between the two companies, and while neither would stand to lose from this arrangement, and both already have games of their own in GOG, the probability of that happening is very low.

They prefer to make no money at all, then let a rival company make money from their property. The only games you'll see from now on are the ones that can take advantage from corporate synergy. Warner Bros. gaming studios making games based on Warner Bros. movies.

This is also the reason why we have a new Lord of the Rings game coming out in a few months, published by WB, yet none of the old LotR games are available for sale anywhere either.