I really wouldn't bother over-analyzing this or reading too much into it. He could literally just be leaving room for the possibility of shipping unknown future titles using the engine at some point down the road.

I immediately interpret it as Forza Horizon 6 already in development lol

Well, that is to be expected. In order to keep up a Forza Horizon release every 3 years, it probably was already in pre-production before Horizon 5 released, and has been in full production pretty much since Horizon 5 released. Will be gaining more and more devs on the Horizon 6 team as Horizon 5's 2nd and final expansion releases and the last few paid cars release, with just a skeleton team left on Horizon 5 to provide the GaaS seasonal updates and other patches.

Edit: Actually it looks like all of the cars on the car pass already released, just the 2nd expansion and seasonal GaaS updates left ahead of Horizon 5 now. Once the 2nd expansion releases Playground's Horizon 6 team will be at full size except for any new hires between then and release. 

I wonder how Horizon 6 is going to go? Did they start from the ground up for Horizon 6 with a customized variant of Forza Motorsport reboot's ForzaTech engine, which was built specifically for Xbox Series/PC development with ray-tracing and such? Or did they keep using the same internal build of ForzaTech that they have been using and lightly upgrading ever since Horizon 2 in 2014? 

There are pros and cons to each:

Starting from scratch with a new Horizon build of ForzaTech based on Forza Motorsport reboots build of ForzaTech would give them better looking and more realistic car models, as well as greatly upgraded physics for those who prefer to play Horizon with the all of the physics set to make them as realistic as possible. However, they would be largely starting over from scratch with car models, reusing some of those already built by Turn 10 for Forza Motorsport reboot as well as using some new car models they made themselves, including some Horizon mainstays which are lacking in Forza Motorsport. Overall car list size would likely be smaller than Horizon 5's was and it might end up taking an extra year of development, with a release in September-November 2025 most likely.

Continuing to upgrade the same build of ForzaTech they have been using internally since Horizon 2 would allow them full access to Horizon 5's car list so that they could add on to it with even more cars and have the largest Horizon car list yet at launch. Development time also would likely be less than if they started over from scratch, release would likely be in September-November 2024. However, some of the car models would likely look a bit dated as they were originally made for Horizon 2-5, meaning they had to be able to run on Xbox One. And the driving physics improvements over Horizon 5 would likely be smaller than the driving physics improvements of Motorsport reboot over Motorsport 7. 

Developer Direct is now 2.5m views.

Persona depression is definitely a thing

I would be surprised if Forspoken doesn't go sale in the next 3 months

Quality. Quality. Quality. Quality.

Keep it up.

Goldeneye 007 HD should have been released on Steam.

Steam’s gonna become the moderator in console warrior claims of Xbox exclusives, or in this particular case with Forspoken, PlayStation exclusives suck