I can't see unpaid DLC happening unless it was as a preorder bonus for other games. In Mewtwo's case, "get both Smash 3DS and Wii U and get Mewtwo!" In a case like Dixie and K. Rool, "preorder this new DK game featuring both characters and get them for Smash!" Isaac, "preorder GS4 and get Isaac in Smash!"
The only problem with GS4 is that would require DLC up to two years out. Which could be possible. More likely, it'd probably be paid DLC featuring Isaac and if you later preorder GS4, if you didn't buy Isaac already you can get him free.
However, him saying "paid" DLC could mean they had some other leftover characters they are finishing up post-release other than Mewtwo (I honestly believe there were more than Mewtwo and IC's), and maybe they're unlocked in the same way you get Mewtwo. By him saying "paid" DLC, all it means is, at this point in time, no "paid" DLC is planned, but free or bonus DLC could be in the works. However, it doesn't mean "paid" DLC cannot happen later.
And if Golden Sun 4 becomes the best GS game ever (which I hope it does when it gets announced), then it woud make up for Dark Dawn's cliffhanger (I loved Dark Dawn, but the ending was terrible).
Also, if it its good sales, than Camelot may do a remake of the original two games to the 3DS with awesome 3D graphics.
All they need to do is market it properly like with Fire Emblem: Awakening. Do that and it will sell well. And they do need to make it better than GS3.
However, I would not want GS1/2 remade. We've already got re-releases, I'd rather focus on making fully new games.
I really really really wouldn't be surprised if the GS VC releases were used to gauge potential interest in furthering the series.
I think they were, however I still think that GS4 was probably planned before GS1 was re-released. Granted, they may have been like "ok, we're doing GS4 right after Mario Golf: World Tour, let's see how much interest is there. We'll release GS1 and see how well it sells. If it sells well, we'll allot a higher budget to GS4." Or something like that.