Thanks for all the replies.

"Why steel?" is a fair question and I don't think I can answer it rationally. I don't think the Downtube bikes are badly made; and I'd say they did not wear out from use as much from the repeated tightening and untightening of the seat post collar. In the case of the 8H perhaps the way the seat tube diameter is reduced at the top introduces a weak spot. At any rate, I have ridden steel bikes all my life with no problems, and have had serious problems with aluminum frames. I won't pretend to be rational about this. I just don't want to deal with aluminum again if I can help it.

I have also dealt with chain tensioners before, and don't want to repeat that experience. I know there are many people who have good experiences with them. I have not. Perhaps they are better mechanics than I; I don't know. Mine was always noisy, and it made changing a flat tire just a little more complicated, and I hate changing flats enough as is.

As I mentioned in my initial post, I already have a perfectly good wheel with a Sturmey Archer XRF8 hub in it. There would be no need to think about a different hub even if there was a better one; but speaking of which, I don't believe there is a better hub. I really really like the XRF8. In fact I like the XRF8 better than the XRF8w I have on one bike; but I realize many XRF8's were defective and many people have had bad experiences with them. But as long as I can keep mine running --it is my third one-- I will.

I do not like the Shimano Nexus 8 speed hub much. I have put a few thousand miles on mine, both touring or long distance riding and riding around town. There's nothing really wrong with it, but I dislike the unevenness of the steps between the gears, as a result of which I have never developed an intuitive sense of when to shift. Granted, I ride the Sturmey Archer one a lot more, so I expect the Shimano one to shift like that, which means I shift the wrong way a lot of the time; but even on long rides, when I overcome my tendency to shift backwards, the unevenness of the gearing continues to throw me off. I mention this in reference to the Tikit; there's no way I'm going to spend $1000+ on a bike with a Shimano hub on it. Premium prices demand premium components. I haven't tried the 11-sp shimano hub, so am not commenting on that.

Nor am I going to go for Brompton's hybrid gearing. The combination of a three speed hub and a two speed derailleur means a lot of double shifting looking for the perfect gear, and is fine on long distance riding but not in the city. I know this from experience; I ride centuries on a bike from the 40's that has that type of gearing system. I'm confident the modern Brompton system is better, but in essence it will be the same.

At present I'm waiting to hear from Yan whether I can get a replacement frame for my 8H. If not, I will get a Speed Uno and hope I can modify it to suit my needs. Even so I may take the broken 8H frame to a frame builder and say "can you make me one of these in steel?"