I did find it a little curious why a lot more people back up the Shovel Knight rumour yet more or less brushing aside the one for Layton....
I mean, you have one rumour about a guy having potential insider info from an unknown source telling him that Shovel Knight is coming. And you have another where an entire voice actor who has been voicing Professor Layton since his series was born saying that he thinks he may have voiced him for Smash 4 during a recent session.... Granted the latter is a little more uncertain whilst stressing that he hopes that whatever he voiced for was really meant for Smash but still. Or I may have missed something of significance in regards to Shovel Knight's rumour that I'm not aware of.....
I guess its like True Blue Warrior said. Two Smashboards Moderators are backing it which probably prompted a few members to back that one more.
It should probably be noted though that not even the mods are always right as a few of them backed that one rumour that more characters where in the 3DS version besides the ones in the ESRb leak which ended up not being true in the end.....
I think the reason why the Layton rumor regarding the whole voice acting deal hasn't seen as much spotlight as the Shovel Knight rumor is because most people moved on from Layton after Miller tweeted that he didn't know if he was recording for Layton for Smash or not. Most people interpreted this tweet as meaning, "Well, looks like we aren't getting Layton after all," and then they went back to speculation until the Shovel Knight rumors started gaining widespread attention.
I've mainly come to this conclusion based on the fact most discussion about Miller having 2 unknown voice recording sessions was here on the Layton support thread. The only times I've seen it being mentioned outside of this very thread was in a Miiverse post and a brief mention on the DLC Character Discussion Thread about two days ago. Even then, I've noticed the more prominent Youtube users, particularly RogersBase and Gamexplain, that reported about Miller "not knowing" didn't explain about those 2 voice acting session details that followed. Not mentioning this detail means that most viewers will think "Well, looks like the Layton rumor is done thanks to Miller's Tweet". There's even very little to no mention about those voice acting session details in the comments sections of either of those videos either. I have a feeling that if some prominent Youtube user uploaded a video discussing these voice acting details, then there would be much more discussion regarding this topic.
Then again, maybe I'm wrong and it turns out there actually is a large amount of discussion about this Layton rumor outside of this very thread in Smashboards, but from what I've been seeing, most of the hype and discussion about this rumor has been pretty exclusive to this thread. If the voice acting session rumor was more publicized where prominent gamers shared details about it so that their fans have something to think about, perhaps we would actually be seeing as much as discussion as we currently have with the Shovel Knight rumor, perhaps to the point that in Smashboards case, there would already be a Layton re-rate day on the RTC Thread where the voice acting discussions are the primary driving force for the re-rate.
But perhaps maybe it's a good think this current Layton rumor isn't as widely discussed as the Shovel Knight rumor, because that would make the element of surprise for a Layton reveal much more exciting for the Smash community.