LC, what you've posted could work for me as well, but if it was a matter of never having another rod again, I would go:
3wt, 8' fast action
6 wt 9' fast action
10 wt, 9'6" fast action
I own every wt from 3 to 10, and a couple of 9's. My 3 & 4 wt I pretty much use interchangeably. I would however pick the 3 over the 4 because when I need that extra amount of finesse, IMO it's a bit better than a 4. I don't do much with dry flies, but if I did, I would rather have the 3 wt. Both to me are "ultra light" and I use them primarily for panfish, with occasional trout fishing. I've caught plenty of bass on both too in some very tiny streams.
I'm primarily a bass & Striper angler. I've caught many bass on a 6 wt, so could continue to do so. It's a good all around wt for bass in the east. Much of the bass fishing & a good amount of Striper fishing I've done has been with an 8 wt. I use the 9 a bit more for Stripers. But again, last rod on earth, I would go with a 10 wt because it gives me the option of going even bigger with fly size, is a bit more weapon against the wind & with larger fish. Same could be said with an 11 or 12, but for me, I've yet to encounter a fish I couldn't handle with a 10, and doubt I'll ever get the opportunity to go after anything I would need a heavier wt rod for anyway.
I also use the 10 wt for LM bass in some of the tidal rivers. It's more rod than's needed for most of the fish, but it shines in the slop & snags with bigger, heavier flies, and makes dragging even a 2 lb bass & 4 lbs of vegetation out from under a downed tree so much easier than a lighter rod. My kind of bass fishing!
Easy, these are my go-to's anyway:
7'/ 3wt slow/ medium action glass with a 3wt DT for small streams
8'/ 6wt medium action glass, this will handle a 5wt and 6wt DT for all purpose trout, a 6wt WF for smallies and a 7wt Intermediate for schoolie bass and light saltwater (bones!)
9'/ 9wt graphite for all purpose saltwater
Yep,
7ft 3wt fast action. Sometimes you need to shoot that dry fly into a 3inch circle at 40 ft
9ft 7wt for my bass and large trout streamers
9ft 12wt that would be for anything that swims in the bay, cobia, bull reds, offshore mahi and smaller tuna, white marlin
With all that being said my 3 rods that I fish on a regular basis is my:
7ft 3wt gloomis imx dry flies
9ft 5wt scott freshwater bass and nymphing for trout
10ft 7wt orvis silver label (I think, it was a present) my go to saltwater flats rod and my Alaskan stick. That rod has beaten up hundreds of salmon and a few steelhead over the years.
Wait wait wait I want a fourth rod I have to have my Spey rod!!!!
These would cover it for me considering I currently do very little salt:
4wt 8'6 (trout panfish)
6 wt 9' (steelhead, bass, shad)
8wt 9' (steelhead, shad, light salt) I would make the a Sage Xi2