At some point I feel like that point of time will have to have its final mysteries fully covered in a game, maybe KH3, hopefully finally in cutscenes.
What happened at Radiant Garden was the start of the biggest main conflict we knew about in the Kingdom Hearts series for a long time. It was a backstory we learned the most about in written reports, and we continued to learn more about that point in time as lore changed. We saw it shift from the villains' origin story to somewhat of a transitional period of BBS to KH- although we never actually got more than a few scenes of the Apprentice Terranort.
There are still some uncertainties about what actually happened back then, and even more keep appearing in each game. Why did Xemnas build the Chamber of Repose and speak to Aqua's armor? What happened with Eraqus' heart? Was Xehanort really faking the amnesia? In this game series, even as far back as the original war over the light is being covered in Chi. BBS 0.2 is covering a similar point in the timeline, directly following BBS, as would the point in the story you want to know about- and I don't think it's out of the question we may get some clues on what happened with Terra-nort-aqus's hearts in a cutscene or two.
Gameplay-wise and just overall though, I'm glad they went with following Aqua through the Realm of Darkness. I'm super excited for it!