IMO, KH3 won't end up like FF XV did, i think that's a specific case of development hell. usually games that take that long usually do so because they're scrapped and started over, usually multiple times. also keep in mind Square is in a pretty bad position right now financially. both their NA and global presidents resigned recently and the new president has gone on the record to say he wants to adopt a new company strategy of "getting more games out the door." once FF XV is done, i think the entire company's primary focus will be getting KH3 out. i'd imagine they'll start transferring developers from Tokyo to Osaka to work on KH3 as FF XV's development finishes up.