I'd love the option to race against the 'fake' F1 drivers (Roth, Forest) offline

Outside of F1 World, I honestly think they should consider adding fictional drivers into MyTeam / Driver career, the driver roaster is just so unsatisfyingly small atm, if you're one of those who dispises adding legendary icon drivers (luckily, I love icon drivers) then it become even worse. You barely had any selection to keep things fresh.

This was literally what I came here to say. 

A few years ago, I was frustrated when the fictional drivers would come in to the career mode.  For example, I had Marie Laursen come in to McLaren and she stank up the joint so I have hated the fictional characters ever since...

But... make them good, or at least competent.   And you have something there. 

I'm one of those you mentioned that doesn't like adding Icon Drivers. It just feels weird.  I'd have Senna, Schumacher and a 70 year old Alain Prost (who also looks 70 years old) racing on the grid and it doesn't feel right.   Now I know in the internal fictional narrative, Senna isn't a Zombie coming back to race and Schumacher isn't in a coma and Prost (when he was in it) isn't a bag of dusty bones that'll turn into powder if he goes too heroic into Sainte Devote but it doesn't look like something that I can extend a suspension of disbelief to, because they're real. They have history and legacy that you actually know.   So I've disabled the real F1 Icons and I have the 4 F3 and that's it. 

Now, in games like Football Manager, I massively prefer the re/newgens to the real-world counterparts.  Maybe it'd be a little trickier to get the same emotional detachment from the F1 drivers because there's so few of them that you feel like you'd notice their absence more, but if the fictional drivers come in and they're actually F1 level (say mid 70's and above rating) and potential to be just as good as the leading drivers after a few years then it's much more believable because you're making their history rather than distorting it like the Icons.  It could not only make the pathetically small pool of drivers actually functionally-sized but it wouldn't really cause any licensing issues neither.

The helmets look better this year now they have sponsors and the like so it even feels like there wouldn't be the usual customisation-style issue where they have the most generic looking helmet imaginable and they don't suit the car.