So, we are getting volcanos?
My idea wa to insert some random volcano using existing lua script - just eyecandy only,
and additionally, for warm-dry climate change, evolve mountains into volcano (it is even scientific accurate, global warming can increase seismic and volcano activity).
But this project is now suspended until 3.0 will be ready.
Generally terrain generation and terrain.spec properties are not supportive for any custom tiles.
I managed to generate Taiga tiles near Tundra tiles and that is all.
It is not possible to generate snowy mountains in cold biome and non-snowy in warm biome, separately
(they look at mountaneous property which is common for whole map, adding cold/warm property would change probability,
but still they will be mixed).
There is lack of something like logical AND of properties.