In super high density areas, fibre is going to be cheaper and faster and more easily maintained and upgraded etc than satellites

I think "super high density" is probably hyperbolic. As density increases shared airwaves become more crowded and wired infrastructure becomes cheaper to operate. I can see wired internet being competitive for a long time. Even in places more like St. Louis than Manhattan.

I choose where to live because I can have two different fiber connections (for speed and a failsafe). How long will it be before satellite internet offers 2gbps symmetrical with low latency at reasonable prices?

The use case of someone who needs two gigabit fiber connections to their residence is exceedingly tiny and would have no bearing at all on spacex's market.

I can hardly imagine a situation where internet access is so critical at a home that you need two fiber lines anyway. I have probably had 2 hours of downtime in the past 3 years with my cable connection.

Starlink is intended to provide 1Gbps service to end users with low latency, especially if you’re accessing sites on the other side of the world.

Are you camping out at the datacenter again?

Providing backhaul for rural cell towers is expected to be a big part of Starlink's business, yes. Same for O3b and Oneweb.