Is it really possible to land e.g. a Cessna 172 until full stop with just G1000 synthetic vision?
I don't think the terrain database is anywhere near that accurate. The resolution is of the order of 100-200ft.
Obviously it could be improved locally, around each airport, but somebody would have to be paid to do that, and it would be quite a task. There are of the order of 10k airports in the world.