Now we're working on restricting short distance air travel within Europe, meaning large airports like this one may become too costly to keep running, if it can't be utilized enough.
Right now it's still only France, but German politicians are talking about adopting a similar strategy.
The French model actually aims to ban flights that have a sub 4h train connection. Meaning the Eastern European nations without high speed rail would have fewer flights affected if this becomes EU policy.
It would cut a lot of flights to neighboring countries, and domestically in Germany.
Quite simply, if you're under 4h train connection you're far enough to justify a flight.
BER is pretty safe on flight numbers.
A railroad investor could look at existing flights and accurately project how many passengers they can expect, since flights would be blocked the second they open their carriage doors.