The only console games Falcom's ever developed are:
1994-1995
The Legend of Xanadu (PCE)
The Legend of Xanadu II (PCE)
Popful Mail (SFC)
Ys V (SFC)
2006
Gurumin (PSP)
The Legend of Heroes VI: Tracks in the Sky (PSP)
About Ys IV... Falcom was originally working on this game, although the system is unclear. Probably PC-9801 as that was the machine they were working on at that time, and all (well, most) of their game releases by that time were PC-9801 exclusive. However, there are two soundtrack CDs of Ys IV music, X68000 style, one of which contains a lot of never-before heard tracks. So one can assume they WERE going to release an X68000 version of the game.
Falcom was also working on Ys IV for Mega-CD. Sega Falcom, to be specific. That appeared to be some kind of division of Sega which was based on Falcom staff, as they made a couple of Mega Drive/Mega-CD ports (Lord Monarch, The Legend of Heroes 1-2, Popful Mail [MCD] Super Brandish [unreleased], etc). I like to refer to Popful Mail, Super Brandish and Ys IV as the Mega-CD Falcom trio. These games would've rocked the Mega-CD had they all gotten released together back in 1993... maybe.
Looks like Tokyo Shoseki (who ported Ys III to SFC, among many other Falcom games) bought the rights for Ys IV and released it exclusively on Super Famicom though. That is probably why the Mega-CD version got canned. I believe TS altered the scenario a bit, though.
As for Ys IV The Dawn of Ys... well, Hudson probably made it because they too wanted to release a new Ys game on their system, but TS owned the rights for the original game, so they simply made their own. Something like that.
Why, oh why didn't Super Brandish get released? All they left behind is one single music track!