The effect of the F-Duct is "supported" i.e. the McLaren will be quick in a straight line. However you won't need to move your knee or press a button - I think they've just reduced the drag. The variable front wing is supported though.
I'm not sure about F-duct, because the game will be avaliable in next month, that means the season of F1 won't be finnished and not every team have F-duct, but maybe in the end of the season they could already have, so the game wouldn't include those teams?
F-duct works quite differently on different cars so I think it wouldn't be a good idea to add it to all. Patches can do it imo if somebody will have it later.
BTW stay ready, if they'll have it, you should set it on a button in specific cars that you can only reach while driving one hand to simulate it properly! lol
Well, considering that it's not meant to be any effort on the driver and can gain you upwards of 3 mph in a straight I would say it could be simulated without any interaction... you can also adjust the front wing and that makes a big difference. If the game had both it would be like a turbo... and could feel odd...