I wish I could remember the source, but I believe I'd read that the reason it didn't get released was because by the time it was ready, the monies to release new games was gone.
Although I don't think the game was finished being localized, I don't think TTi would have put much effort into it. They seemed to favor cuts over actual localization towards the end. They probably would have either given the PCE character an original name or left it as-is. Aside from all the literature TTi put out talking about the "PC Engine", it was noteworthy enough in Western circles for Konami to call it by name on the SNES Drac XX box.
Fantasy Star Soldier definitely isn't worth a pressing, any more than it's worthwhile hacking any other PCE game to remove content and change a single logo for a pressing.
Edit: forgot to mention what inspired this post in the first place.
Doesn't New Adv Island have a white PCE pad in it? Like they couldn't be bothered to even do a color swap?
I don't believe it was ever fully "ready" they still needed to do some sprite changes to change the PC Engine sprite to a TurboGrafx or something Westerners would recognize among other things. They basically just changed the title screen and removed some of the cutscenes in the versions in circulation.