My passion for the franchise comes from the passion of the developers and the team behind it. There's an unbelievable amount of passion and ambition that is poured into each and every title that they release- they simply don't have enough time to include all of what they want to include! It's what fuels me to document the games on The Cutting Room Floor with the sheer amount of unused and hidden content that isn't in the games simply due to time constraints. Had all of those executive parties left PoDi alone to develop their games for a few extra months instead of pushing for holiday sales release dates, then the games might have been significantly different experiences than what we know them as today, which are already great experiences in my opinion. Just like great food, great games take time to make, and if they don't have the time they need, then the leftovers either get saved for later...or scrapped forever.
It's what keeps me interested in the franchise even in present day. Even though the direction that Gran Turismo Sport took is a radically different approach than what most fans were used to, the passion and ambition is still there. As time goes on, they're working to include as much as they can, and with the new distribution model that can be said was "invented" by Gran Turismo 5, new content is being added to the game on a regular basis, and you really don't know what you're going to get next!
Special Stage Route X is the first "classic" or "previous generation" course to return from Gran Turismo 5 and 6, so it's not like they've forgotten about and scrapped every "previous generation" course they've ever worked on. There's some original masterpieces that must have taken great efforts to develop and polish at their time of development, and surely they weren't going to be only included in two titles on older hardware, right? Surely that isn't the case, right!? It makes you wonder!
I can't say I know the future of the franchise, but that's what makes it so endearing. You don't know the next turn that Gran Turismo is gonna make on its course, but whatever the case, it'll probably surprise and delight you, or at least, that is Kazunori's best intent, I feel.