I have very mixed feelings, too. I am old enough (just about 61) to say, "if I can ride, so can you," but, maybe when I'm 85 or 90? I'd rather just get a nice upright bike and do less hills...
I have seen exactly one while I've been riding. It's pretty much a cycling mecca around where I live, so I doubt I'll be seeing many.
DH saw a guy on one, last year when he was riding to work. He couldn't figure out why some guy in jeans was dropping him, so when he caught him, he found out. The guy appeared to be neither out of shape, overweight, or super old.
A few years ago, I was doing the bike valet duty at a farmer's market and some company was demo-ing e-bikes. They looked huge and heavy. Meh, if someone wants one, it's fine with me, but I will not be getting one. I ride with too many people in their 70's to think it's just for older people!