It's great having multiple gamemodes, don't get me wrong. And Warframe has good ones. But let's be honest, most of them are not very engaging, are half-backed, or even feel unfinished. Just adding gamemodes and not expanding and polishing already existing ones is a waste of time and resources. Warframe is almost as bad as Kingdom Hearts 3 when it comes to that.
In Online Games it's important to add new Gamemodes/Minigames right into the core gameplay or nobody will play it after like two weeks. Archwing did that kinda great. Cars are a cool Idea. But if they should add cars, they should expand the core gameplay, so People will actually play it and also buy Skins for it etc. because when it's a part of the regular Gameplay, of course People wanna spend Money on it.
It just needs to be be a new Mission Type with new Maps that mixes the Core Gameplay as a Warframe with the Car driving Gameplay. For Example, first you need to drive from Point A to Point B while you get chased by enemies. At Point B you'll need to steal some Supplies and fight enemies with your Warframe. After you got the Supplies you'll need to get out as fast as you can, because there's a time limit and enemies chase you again. And the Mission should be playable in both solo and with other players, just like regular ones.