It's not impossible, but Switzerland's geography means tunneling is involved in adding capacity which makes it very expensive. Also the beautiful synchronisation of a country-wide integrated timetable where you can reliably get between any two places in the country with connections that always make sense is a point of national pride.

Japan, Taiwan and China all added dedicated infrastructure which took a long time and cost a fortune (vs the shared tracks currently used for intercity/regional/European freight). Tokyo accepts famously absurd levels of overcrowding during peak hours. Deutsche Bahn in Germany is widely thought of a joke due to chronic underinvestment meaning on-time trains are surprising.

That said, these technical concerns have nothing to do with the 10 million proposal. It's worth asking why a camp that spent decades opposing sustainability legislation has suddenly discovered the word now that it can be pointed at immigration.