Oh snap! Very exciting if true. For me, Mario IS my gaming origins, Maro Bros/Duck Hunt was the very first game I've ever played, and still love the series to this day (less so on the 3D front but still enjoy it). So much potential for this.
One way Nintendo could handle this which I think could be awesome would be to have 2 or 3 separate "Mario All-Star" bundles - one with the older 3D titles (Mario 64, Sunshine, Galaxies, 3D World), one with classic 2D games, and maybe even one with the handheld games remastered and given the Zelda: Link to the Past Treatment. One of the most underrated/overlooked Mario games for me was Mario Land 2: 6 Gold Coins. Remember playing my dad's copy on his old Game Boy and really enjoying it. I've also been looking at an excuse to play Mario Sunshine again, as it's been like 18 years since I picked it up, and I have always felt like it's one of my least favorite Mario titles, but I feel it's high time I give it another chance. That game also screams HD remake.
One thing that's unclear that I'm really curious about is if we're just talking up-ressed graphics and maybe a bit of new content or full-blown remake. Either way should be awesome, assuming it's true!