Makes sense why they remove Train, honestly. Mirage and D2 can't be removed, because they are the most played maps, all over the world and even over 60% on Faceit and FPL. It could actually kill the game because of a sharp decline in audience, if those 2 got removed, regardless of how much hate they seem to get. They are the main maps in solo-queue and also in countries with smaller CS pro scene (huge part of CS community).
Train is the 2nd-least played map in MM and Pro-matches, the lowest being Vertigo. But Vertigo is new and always reworked, so they won't remove it yet. Train is the same since 8 years, so they removed it. The addition of Ancient isn't bad, and it will surely go through major upgrades, just like Overpass. The colours, site physical aspects, features, etc, all will go through improvements and tweaks.