Well, you can still find 6 and 7 speed freewheels and 7 speed cassettes, so I would say the "but who knows for how long?" argument is moot. If you're talking downtube or bar end shifters, those are pretty durable and I wouldn't expect to replace those for the life of the bike.

6-7-8 speed components are pretty durable. Chains and cogs last many years. When you get up to 9-10-11 speed stuff, though, it simply doesn't last as long. To fit that many speeds, and also because weight is more important for more recent drivetrains, chains and cogs are made out of thinner materials and have a much more limited expected life.

If you go up to 9 or 10, you will love it at first, no doubt. If durability matters to you, though, you might be disappointed.

On one of my bikes, I did an upgrade from 6 to 7 speeds by simply putting a new, ramped 7 spd freewheel on the bike. Even though my shifter is still friction, the shifting is very clean, almost like it was indexed. Best of both worlds.