It's been a while since I watched this video but the proposal is for 5 storey high developments along transport corridors that do not tower over suburbs like high density developments, but which also serve to engage with street life more effectively than existing low density.
https://www.youtube.com/watch?v=ZYJpdH-VGwc
It can be done. But obviously needs a departure from existing low density suburban sprawl, and a tight control over overdevelopment. But it can actually result in better amenities, faster transport, for residents.
1) build high-rises
2) build more metro lines
Look at Tokio or Shanghai, as an example.
Shanghai has lots of high rises; well, they are mostly 30 story apartment buildings that can be reliably built with concrete and unskilled labor. Yet, there is a lot of speculation market in the China so prices are still high even if supply expands (and many apartments are empty because they are just being used as speculative investments). One of the reason I didn't look at Shanghai was commute times (Microsoft's Shanghai office is in the boonies vs. Beijing where the office is at least inside the 4th ring rood).
Right, but only because of the seismic activity, from what I know. In most other places that wouldn't be an issue.
Nevertheless, Tokio is still relatively dense with tightly packed mid-rises, and actively building.
Maybe I'm misunderstanding what you mean by "high rises", but I don't think this is true. I live in Tokyo, inside a 10+ floor building, that's surrounded by similar buildings.
Just off the top of my head, I can think of a lot of places with multiple blocks full of high rises, such as Ginza, Shibuya, Akihabara, etc