Component life span on a turbo

As per SimonAY, I would be more concerned with corrosion from sweat. The bike I have on the turbo has paint flaking off all over, lacquered brake levers are flaking, bare steel parts are rusting.... It's been on there for 6 years constantly and I didn't keep on top of wiping it down when I started. The paint flaking started and now.... Well, I can flake paint off with my fingers.

Sweat catcher and a towel I reckon for anything you want to keep in a rideable condition.

The steel levers in the shift mechanisms of my Shimano 105 (5800) shifters are extremely corroded due to sweat. I make sure I wipe them off after each session since I noticed.
If you clean and lubricate your drivetrain as you should I'd say sweat in the shifters might be the more serious issue.

You may get no road grime in the lube but I'd suggest that it's actually metal swarf from the drivetrain that does most of the wearing-down of surfaces. It becomes a very effective grinding paste. I believe a trainer will also probably generate about twice as many chain link articulations per hour due to fairly constant pedalling.

I've switched to waxed chains now and change every 300miles, ish. Even then the wax is a bit "blackened" even though it's only been used indoors. My SPD-SL pedal spindles are rather rusty and I'm fairly sure sweat ingress prematurely annihilated the non-driveside pressfit BB bearing (there were no remnants of bearing balls and one of the races snapped in two places, big/deep grooves in the surfaces and a lot of red/brown gunk), driveside bearing is fine.

Chain cleaning, lubing, checking and replacement will keep things in line. You're likely to notice when cogs are worn, having a spare 105 cassette (and chain) ready may save you trainer down time. 105 parts aren't too expensive I'd say, probably not much to worry about right now but sensible to plan for replacement before too long.

Chains don't last as long for me though clean and lube frequently. Gone in about 2k km rather than 3-3500 km. Pedalling the entire time doing workouts so higher than normal wattage (still not much...)

Consensus seems to be that when on the turbo you're always pedalling, thus an hour's ride on there is harder than an hour outside where you'd maybe freewheel/soft pedal downhill for a certain amount of it.

I guess by the same token if you are measuring drivetrain wear by kms ridden then you'd expect turbo use to incur wear in fewer kms than road use as you'd always be pedalling pretty hard. 

Not seen anything to quantify wear rates though.