Do you really think Nintendo said "ok Sakurai you have to pick a rep that belongs to Microsoft"? "Hey Sakurai, you know what company everyone knows? SNK."? Dragon Quest, again, is the safest bet in the list that Nintendo said "this is what we're doing" and Sakurai ran with it to the extreme, especially since we have shaky evidence that Dragon Quest might have been intended to be base game content. Everything else doesn't add up as a Nintendo pick.
A long time ago I said that the most likely scenario is that Nintendo had (and likely still has) a focus group for Smash DLC and I still believe that's the case. It makes more sense than an exhaustive list or Sakurai getting an email with a name in it and deciding if he likes it. A team of people probably did at least a year's worth of research on gaming trends and compiled either a list of franchises or genres, and maybe from that they created a list of characters, from which Sakurai chose. RPGs are kind of on the comeback, retro is in, fighting games, or more generally, esports are growing by the day. What other trends would a focus group (read: soulless cash grabbing suits) notice?
[X] Doubt
Not that it isn't possible, but given Fatman's commentary on insiders and my own personal feelings about them, "stop guessing lol" is a subtle "you'll absolutely never get this character and I wouldn't tell you even if you did". If Fighter 5 is any character commonly speculated, I'll be floored.