This is how a 2019 F1 car will look like :
To be honest the 2018 cars look good even with the halo but some little changes could make them even more good looking.
First, change the T-Cam and remove all the useless cameras like the shoulder cam for example, due to the halo. Look how the T-Cam is big in F1 compare to Formula E for example, it could be a lot more inconspicuous.
Secondly, the nose and the front wing neutral section. The front wing neutral section is quite useless so why not removing it, or elevating it to be a part of the nose cone.
Last but not least, add a windscreen to the Halo.
This is how these changes could look on a 2019 car :
If you have some ideas about little changes to make the cars look better, feel free to share your opinion and i will change the photoshop to try your ideas