The bolded is why I'm curious to see if these HD remake rumours are true. As SA1/2 had some real potential for how Sonic could control in a 3D space.After having to go take a serious look at how your attempt to move "forward" fell flat on its face in Forces (aka Generations 2 by another name), I would hope even more so now that Iizuka is willing to go back to Adventure, and mine those old games for ideas while you set about remaking them. You get to revisit games that people actually liked (or still like, in other instances), and if they're received well? Then by all means, expand on those things that worked so well and jettison those that don't. (And hopefully, have Flynn on hand to make the character dialogue sound much more natural!)
Also, it is hard to take what Iizuka states at face value either, did he not say that it was unlikely that they would bring classic Sonic's design back after the negative reception of Sonic 4? Then Generations was announced shortly afterward.... I cannot find the source on this, but remember this was floating about during the pre-Sonic Colours hype.
So it would not surprise me if they do go back to the Adventure gameplay style for the next title (or at least merge it with the Generations Modern Sonic Stages in some manner).