oil does not 'go off' as such... yes it can pick up chemicals that you don't want sitting in there for years on end, but like your brake pads, its a wear part, so if you're not doing the service miles, I'd have no problem keeping it in there longer...
I had a 1200 Bandit that used to do 1500 miles a year if it was lucky... I'd put Semi-Synthetic in it that would easy last 10K miles.. so I'd change that every 3 years so well within its lifespane....
I also have a V8 that I run of mineral right now as its re-bedding after a re-build... I'll only do 1K with that before it gets changed... guess what I'm saying is if the oil life is 10K... then leaving it in with reduced annual miles to half that won't be a problem at all...