Data Riku contains all the information but he isn't necessarily consciously aware of all that information. Data Riku might not know any of the information so he might need to be told about the information by someone else. Data Roxas or Data Namine could just as easily deliver that information to Riku.
During Coded he was much aware of the normal data of the journal though and after the riddle was solved the additional torment data was added as well due to Data Sora.
Data Naminé can't deliver anything because she's gone, she was made just for the purpose to convey the data on the tormented and then faded away.
Data Roxas is also not an option because 1) he didn't know of the crucial information the Data Naminé had, he only knew about his own pain and choose
on his own accord to test Sora, that had nothing to do with the torment data or Data-Naminé and 2) he merged with Data-Sora in the end.
Yensid just has a special way of explaining, unlike Mickey Mouse who has been nothing purposely vague in any explanation he has ever given.
True that, Mickey apparently isn't the brightest explainer around, but why would Yen Sid now bother them with information about their second task
after the Mark of Mastery?
From the Data-Naminé Mickey also knows that Ansem the Wise hid something inside Sora's heart and DDD's main purpose is to find out about that data and investigate it...another hook-point to put Data-Riku into the story since he's a data-expert.
Well I'm not necessarily saying that Eraqus will completely return (though I suspect that will happen). I feel very strongly though that he will at the very least have a more positive fate which means the story will need to readdress what became of Eraqus.
Geez, I'm only cautious with these "completely return" topics since these tend to spark intense debates every now an then, but I can live with either way.
*shrugs* Who knows, maybe he'll play a role in finally removing Xehanort's heart for good, aiding his final demise in KH III which will also prevent his full return. I'm relatively open on what purpose he's given as long as it goes beyond mere fanservice-cameo.
Well yeah, each BBS protagonist endured their own version of horrible suffering for about a decade, so obviously I know that can't be erased (well in the KH series it theoretically can... but I don't think it will). I think the protagonists deserve everything to be put back how it was (except for maybe Terra).
They can get a second chance and their pain be stopped, yep, but not undone except if Nomura really introduces timeline-altering time travel.
That's what I think as well. However, what's with Terra? It's not like he wanted all this and he also fought on against MX at least mentally for all that time, not to mention the BBS-Trio is so closely knit that if only Aqua and Ven receive their comeback they would be probably heartbroken if Terra doesn't.
That could have just as easily been explained by Terra's heart gaining the strength to resist Master Xehanort on his own. Nomura could have created any excuse he wanted in order to give Terra the strength to resist Master Xehanort on his own. Nomura didn't need to keep Eraqus' heart around just for that basic function.
Well, when asked about the additional heart with Terra I remember Nomura saying something about we put in a bunch of foreshadowing.
Foreshadowing for what, well, take your preferred pick, lol.