Amy I have to differ with you on this statement. I have a mid drive speed (28mph) pedelec with no throttle. I weigh 210 lbs and ride an average of 500 miles a month. I have put just over 5,000 miles on my Bosch powered bike since it was new in July. I keep the chain clean and well lubricated and measure the stretch periodically. I don't let the chain "stretch" get more than .5%. I am riding on chain number 3 at this point. My chain has never broken. A good KMC chain is a $11 item that takes about 10 minutes to replace. I do carry a quick link for repair on the bike but have never needed it. I would still prefer a belt over a chain as all that maintenance goes away. The 2018 bike had everything else I wanted but not the belt. Of course this year's model includes the Gate carbon fiber belt. My point is that a properly kept chain that is cleaned, oiled and checked for stretch regularly is not likely to break on a mid drive bike.
Also, what maintenance are you speaking of when you say "belt-drive mid-drives need maintenance"? I have not seen any reliable information that says mid drives need more maintenance than hub drives and frankly, to say that hub drives need no maintenance is just not true. All electric motors are subject to failures for various reasons regardless of how they are used. I think the best that can be said of geared hub motors is that they are so low cost that it is usually cheaper to replace them than try to fix them. For that matter, this is what happens to a Bosch motor when it has a warranty issue.