There's 3 pokemon I want to see as GX'S.
1. Greninja-GX. This pokemon is my personal favorite ever. Greninja's such a cool, brutal pokemon. I imagine this pokemon having HP250, and a high attack in which is playable like the Giant Water Shuriken move all the way back in BreakPoint. You can give Greninja it's former glory by making it look appealing.
2. Toucannon-GX. I feel there's more Alola pokemon that could get GX'S. I feel Toucannon could get a GX in SM4. I would love to see a Toucannon-GX. It could be so powerful and appealing.
3. Sceptile-GX. I feel like there could be a special set celebrating Ash's Kalos Journeys. I mean, his Kalos Journey was awesome. I feel the 2 main GX'S would be Greninja and Sceptile-GX and others like Salamence-GX and Talonflame-GX. those were my 3 GX wishs