That story from Verge is interesting but I wouldn't read too much into it. First of all, like Draxal has said, it's not up to some young director to decide whether to do remakes, let alone which one to remake of. Secondly, the reason quoted is merely "it has not been released outside of Japan" and which nothing on FE6's own merits; it's not like FE 4 and 5 are any different in this regard. It's probably just a random answer to a random question.
Anyway, I do think FE6 is a good candidate because well, Smash. The awareness and interest is there, plus the connection to FE7 which is the first to the west and still pretty popular to this date. However for me personally, FE 4 and 5 definitely takes way higher priority.
BTW, two additional takeaways from this story:
1. This director guy graduated from university in 2009, that means he's pretty young for a "director", not bad at all.
2. They mentioned the name change and not calling it "Gaiden" outside of Japan so that people won't be confused. That's nice and all, but fact is, SoV is also not called "Gaiden" in Japan. It's called something like "Echoes: Another Hero King" in Japan so that point is pretty moot. However, the difference in naming between Japan and the west (not just the mere fact that they are not called "Gaiden") does mean they have put in some thoughts. "Another Hero King" is clearly a reference to Marth being "the one Hero King". However, Marth only becomes the "Hero King" of Archanea in Mystery (FE3) book 2, or New Mystery (FE12), both of which never came to the west. What the west gets is only Shadow Dragon, which ended with Marth as the Prince/King of Altea. As a result, calling Alm the other hero king in the west would have been inappropriate or confusing.