This is how I feel about the current fictional tracks:
Bernese Alps - As it is now, it would get more variety with times of the day/weather, but it needs to get more realistic (narrower) and have more technical sections, and maybe connect to a road for timed hill climbs. Stay or go? Stay but with changes.
Dubai - That has to be the most lifeless desert I've seen in a videogame, it's long and boring, and with the new impact of surface temperature on tires it would only be realistic to run at night. Stay or go? Go.
Maple Valley Raceway - I'm rather indifferent to this one, not great, not terrible IMO. Again, weather/time of day will provide variety. Is already confirmed, so it stays.
Prague - I liked the novelty of it in FM5, but it has worn off since it has remained basically unchanged in FM6 and 7. I would love a true street circuit like Sochi. Stay or go? Stay with a proper short circuit, dump the long (unrealistic) circuit.
Rio de Janeiro - The same as Prague, It needs to be a true street circuit with proper pit stops. Stay or go? Stay or replace with a faux Monaco.
Test track airfield - Please just kill it. Replace with a true test track like Fiorano, Weissach, or Ehra-Lessien.
Top Gear - At this point, it would be fictional because it was demolished. Replace with the Eboladrome, please.
Brands Hatch - Brands Hatch exists across all the multiverse, definitively the best fictional track. It stays.