I was about to point this out; maybe it’s pedantic but this is an engineering matter and pedantry is important. Chains of this sort do not stretch; the side plates are not under anywhere near enough stress to lengthen them. Well, I’m going to assume that you’re not using a small bicycle chain on a real 240hp motorcycle; possibly that would in fact stretch the side plates, briefly, as they turn to toffee. Simple back-of-an-evelope reality check - if the forces in play were enough to actually permanently deform the side plates, how would the pins (much smaller cross-section) possibly survive transmitting that force?
What happens is the pins and rollers wear over time, depending on lubrication, power load and so on. At least for modern motorcycle chains that wear is extremely small with even cursory lubrication by the owner. I’ve had chains last … well, goodness, seemingly forever. Yes, eventually the small rotations back and forth of the pin in its socket within the side plate will wear a small amount off the plate and pin. Summed up over the entire chain that tiny wear will make the chain length a bit longer. It’s wear, not stretch.
On a barely-powered veloci-hipster like this I doubt there is much more than 1kW in use and you could get away with a bit of string to connect the motor and rear wheel. I really doubt any of these will get enough total usage to wear anything expect patience.