The main problem as I see it is the inner cage plate doesn't come up high enough. Well that and the weakness of the second parallelogram.

Here's how I fixed the inner cage plate problem, by replacing it with a piece off a Suntour (a Cyclone I think).



Secondary advantage, it lets you take the chain out of the pulley cage without breaking the chain or removing one pulley. Like old Suntours of the V-GT style, only the opening is in back.

To head off the inevitable questions, no I don't remember how I did it exactly, so I can't give instructions. I did it about 45 years ago.

I think I can say it works though, because the chain never derailed off the pulley after the mod. Though maybe it wouldn't have anyway — they can go a long time without trouble even as-delivered. So I can't prove it's my mod that's responsible for the long streak of no derailing incidents.

Here's Mark Stonich's version:I think he brazed the extension on, which limits the usefulness to only those people who can braze, and only works on the Eco not the titanium one. The Ti one could be TIG welded, but it needs a back-purge, so even most people with TIG welders would not be able to do it without making or buying extra purging equipment. Unless they're already making Ti frames or parts. Hey that's an idea, bring it to someone who makes custom Ti frames. Maybe they'd take it on if they have time and if they would find this quirky little project interesting. (I know, I'm dreaming.)