A lot of people are responding to this saying that "it can't possibly ever happen!" , when:
1- FF7 remake itself was in fact in development hell, was developed by cyber connect 2 before they scrapped their game completely, and it took FIVE years just for the "first" part, when it was clear that they intended it to release it was sooner, no one in 2015 was like "yeah first part is releasing 5 years from now its only natural, that will only cover about 15% of the original game and will be mostly linear"
2-Life is unpredictable and nothing is guaranteed, MGS5 was not a complete project with missing chapter despite the time it took to develop, was even kinda split into parts if counting GZ, Half-Life episode 3 isn't happening either despite them actually announcing it in the past during episode 2 release, along many many examples.
3- but let's just say that "Those are different circumstances from different companies " or whatever, Square Enix themselves had similar experiences in the past, KH3 took many many years, and even then it released in a sorta not complete state and you had to buy the 30$ DLC -can even cost more in EU for like 36$ depending on where you live- to get the complete experience, everyone knows about FF 13 versus cancellation , but let's just say it re-emerged as FF15, people are forgetting that the latest DLC plans for FF15 was cancelled as well mere 2 years ago! And that game was one of the best selling FF games too and yet they cancelled planned DLCs without a problem.
4- not even mentioning the fact that FF15 itself was a "project that was taken over by a different staff" and that was one game , imagine 3 games -at the very least!- and the first one took 5 years, with later parts being more open and have even bigger worlds and open world, how many years it will take? Will the original staff all remains during all those years? Without exhaustion or someone quitting or getting sick or anything? Staff are not immortal, they are still humans and anything can happens during that time.
5- Technically even FF7 Remake is a "project taken over by other staff" since cyber connect 2 is not even involved anymore .
so...yeah, that's a real possibility that can happen and it DID happen in the past, not something "stupid and unrealistic", not saying it would happen but it COULD, shit happens all the time.