Final Fantasy never had a consistent growth though. 7 was its big moment, but ever since, it's been kind of randomly declining and growing. 7 was a significant growth over 6. 8 declined. 9 (a fan favorite) declined much further, X was a significant growth, 11 was comfortably the most successful game in the series but it's an MMO. 12 declined. 13 grew but the sequels (just like X-2) are among the worst selling games in the series. 14 is by far the most successful (but it's also an MMO). 15 saw a growth over 13 and was arguably the 2nd or 3rd most successful offline Final Fantasy, 14 expansions are very successful. So it's all over the place until 7Remake and later, which are declining but haven't been ported yet to Xbox or Nintendo platforms (or even PC in the case of 16 and Rebirth). I think 16 will be the worst selling non-sequel in the HD era when all is said and done, but Rebirth and even Remake have a decent potential for growth even though one is a "Remake" and the other is a "Remake + Sequel".

The short of it is FF never had its BotW or God of War 2018 or Monster Hunter World moment. One could argue that the original FF7 was that moment, but gaming just wasn't as big as it is today. PS1's best sellers didn't sell nearly as much as today's best sellers.

Unfortunately, it'll take several years of consistent quality + a miracle/luck for it to find a growth similar to modern Zelda, or God of War, or Monster Hunter or even Resident Evil. A lot of things are going against it.

I'd bet on the opposite. FF16 is already doing better than Rebirth and if anything the latter should have shorter legs as is usually the case for sequels. A slightly better reception won't do much for it unless, somehow, it lucks itself into GOTY.

Rebirth has just too much going against it, being the second part of the remake of an almost 30-year-old game filled with Compilation references and nonsense Nojima plot points.

Rebirth has a notably better reception ("significantly" among series fans), not slightly, than 16. But yeah I wouldn't rule out FF16 beating Rebirth (If reception was the be all and end all, FF9 would have sold a lot better than it did), but I don't know if it will outsell 13. I think the writing quality of the 3rd "FF7 Remake trilogy" game could have an influence on Rebirth's long term sales, although I don't have faith in the team's writing whatsoever, I think it's a minor factor regardless.

But even if the trilogy's story conclusion sucked, I think Rebirth is going to sell more at least on Nintendo platforms than 16, and it will also get a sales bump when the trilogy concludes. I for one originally intended to skip the trilogy until all 3 games are released, but Rebirth's "Twin Pack" changed my mind. Essentially, I skipped Remake and bought Rebirth!

To be fair, 'series fans' aren't exactly a very large contingent of people nowadays, and 16 did have more newcomers as per SE's admission.

Besides, even assuming both games are ported to multiple platforms, the sales of FF ports and remasters aren't exactly stellar, with most (including, apparently, Remake) not cracking even one million in any given platform.

Well.. most ports came out quite late to Nintendo platforms, like multiple generations late. And a healthy number of gamers are switching from PS to PC which is growing huge. So as time goes, software splits should change in favor of PC and Nintendo platforms. Port sales will not be as insignificant as before.

I admit that Remake seriously underperformed on PC. Hopefully Rebirth does better, as more and more people are now aware that they no longer have to wait too long to have their favorite console games available on PC.

That is so true.  Back in the day it would be like years before a console game came to PC.  An major example of this would be Halo 2. 

Remake also runs like shit on PC. Square is good at making bad decisions.

huh? I just finished remake yesterday on my laptop, run super smooth, 60 fps, never had a single issue. (steam version)

It may have been patched since launch, but there was frame rate stutter issues back in the day.  

Well, if anything the split has become more lopsided in the past decade. FF13 had healthy sales on Xbox and PC, FF15 a bit less, proportionally speaking, and Remake (and Kingdom Hearts 3, for that matter) even less so.

I think the same thing I said as to the relative lack of legs on FF titles applies here: the vast majority of the fanbase is quite old (30s and 40s) and has disposable income not only to buy these games at full price but also on whatever platform it's launching on.

So what you said could happen, but it would need to build a fanbase from the ground up on those platforms, so it's a long-term prospect depending on WoM, quality, promotion, etc., and not in any way guaranteed.