22 years on a Tandem has worked pretty well for us (this is our second one).
I will typically either do my TR interval ride before hand if she wants to just go for an endurance ride or use it as a warm-up ride if she wants more of a tempo ride. When she wants to do intervals then that usually is all the TSS I need for the day.
Regarding e-bikes, I just spent 3 days chasing my 78-year old dad who was riding one. He got a good workout and was able to do the 3 hours rides I had planned with me. So win-win.