The Lexus IS300 or Toyota Altezza would be a great addition to the Horizon series, not only for power potential but for build potential as well, the car has potential to be turned into many different types of setups and tunes, adding variety to the game. There are a calculated 0 down sides to adding the car in the game and would totally be worth the effort of collecting licensing and permissions. The IS300 and Altezza also have a lot of after market customization content, which would work to enhance and strengthen the fairly weak aspect of the game: Customization. Players are always searching for the most unique and special-to-them vehicles and this car would definitely fulfill that need for many of the players. These 2 cars have an excellent reputation in the real world, and have an extremely minimal amount of opposers, which gives it the upper hand in why it should be added as the negative reaction from the players of FH5 will be very little or close to none. Another reason is that the Lexus IS300 has made its appearance in the Motorsports series, meaning the players will have at least a little familiarity with the car and can in turn motivate players to return after the car has been excluded from both series for a generation of consoles or two, especially since it would be one of the first appearance of the car (licensed) in a free-roam type game. Mentioning its appearance in older iterations of the Motorsport series it should be noted that new players to the Forza franchise do not have access to the older content and games which include it as the games are not backwards compatible on any newer gen console. There has been a petition floating around for a while aiming to convince Playground Games to add the car to the game, and as of writing this there has been a confirmed 1.5k+ signatures on the one petition, so there definitely is a good amount of demand for it in the game. Speaking of demand, even if the car was added as a part of a payed DLC or Car Pack, said DLC/Car Pack would attract the players to purchasing solely to obtain the car in the game, meaning there is some profit to be gained from the car, whether that be from game sales or DLC/Car Pack sales.
In conclusion, I think the Lexus IS300 and/or the Toyota Altezza would definitely be a great and welcome addition to the game.
great cars, quite rare on the road… only saw one once, the rest were the 200 or 250… the later model is not bad too, think it was the 250F…
i owned a LS400, a very old one… it was THE best quality engineered vehicle ever imo… sublime, strong, reliable, very well built… think in 22 years it needed a rear spring & o-ring for p/s reservoir… and a dashboard illumination fix… but it was cheap if you avoided Lexus 
22 yrs and that was all that went wrong with it… amazing…
The engine was used in racing i believe, or one of its variants later on… and a plane !!!
i think the 4.3 conversion in toyota is the same one… probably…
the IS300 would be good addition, with a choice of custom aero & skirts
The LS400 would also be a welcome addition along side the Altezza, maybe in a car pack? or a festival playlist with other cars of the same type.
I have no idea if any of the Toyota UZ (V8) engines are in FH5 at the moment or not, however if it isn’t, it should 100% be added alongside the 3S-GE from the Altezza
i think i saw a 4.3 V8 or V10 when messing with tunes once… i presumed it was the last UZ or whatever followed it… i was looking for the 4.0 but its not here…
the 400 wouldnt suit the tracks here the gs300 is ok, i made mine look like the LS400 white/silver 2 tone its public listed
I just ended up with the 400, it lasted so long i didnt get around to buying others… the IS300 had a different kit than normal IS models and maybe twin pipes too ? that was rare back then for smaller cars.
They even started a craze of the ‘copy’ custom lights you could buy for some cars you saw VX astras with ‘lexus lights’ a little legend