It was a more recent interview that made the rounds a couple of weeks ago. Well, it made the rounds recently; it may not have been a recent interview, I don't know for sure on that one. Either way, it made the rounds a couple of weeks ago and he stated that they had a number of characters planned, but were cut for various reasons. Several people brought up the notion that that's why Isaac isn't in the game, and some even said stuff like "GS4 deconfirmed" or something like that.
The only problem with this issue is that when Isaac was cut (if he was), then it likely happened before GS4 was put into development. Sakurai may have very well been in contact with Camelot, and possibly considered Isaac as playable due to Dark Dawn being rather recent before development on Smash started (2012), but then 2013 came around and no signs of GS4. By late 2013/early 2014, Sakurai might've already put Isaac on the backburner, and GS4 likely was not planned until as early as the VC re-releases, and as late as when Mario Golf: World Tour was released.
As such, the Sakurai interview doesn't really mean much for GS as a whole, and might even be a boon, since he confirmed the roster was finalized in 2012 (barring the late clones) and additional characters were cut further in development.