I’m yet to buy this game, but will look to buy it soonish.
I have played Forza, 2, 3, 4 and horizon and cannot believe the Lexus IS300 / Toyota Altezza is not in 5!
Basically I own an Altezza, and am getting the car wrapped in April this year. I wanted to design it on FM5 but of course it’s not there! Really annoying 
I would do it on 4 but I sold my 360 to fund and Xbox One!
Any news on whether these will make an appearance this year?
Fingers crossed
There is no official word on any of the cars they will add or when. If you would like to see a particular vehicle make it into the game then request it. You can post the cars you want to see in the Forza Motorsport 5 Car Wishlist thread.
Would really like to see the altezza back in the forza series too, whether in FM5 as dlc or in 6… Never owned/driven one in real life, but was my very first car in the first forza and it served me well. 
Anyway as fyerball said, best you can do is post it up in the car wish list thread. If it doesn’t show up as dlc in FM5, I’d say it’s a pretty decent chance that it’d come up in FM6 at least. Just my complete guess though.