After watching the 12v LED lamp tear-down video Kim posted, and reading up some more, my thinking is currently(!) along these lines:
I noticed that some 'transformers' eg 12v DC 6w units designed to power a single 5w LED make claims to produce lower flicker, and greatly extend the lifespan of the LED lamp. They don't seem to offer up any explanation or substantiation of these claims, however.
But looking at the schematic in the lamp tear-down video, the input stage is a straightforward discrete bridge rectifier, and large electrolytic smoothing designed for 50Hz, when running the lamp from a 12v AC supply.
This cap is probably the principal point of compromise and failure in the design, I'd have thought.
It will likely have a fairly poor ESR rating, and its voltage rating will be close to it's operating envelope I expect.
So with a 12v AC supply, I'd expect the 'DC'-ish supply to the current regulator to be fairly poor in terms of 50Hz ripple, which might account for visible flicker.
It would depend on how well the high frequency current regulator is able to deal with that.
i can imagine there might be potential for beat frequency flicker, too.
Running such a lamp from a 'clean' 12v DC, the electrolytic cap really doesn't have anything to do, so it's compromised spec will be much less of an issue. I can see how this might extend the lifespan of the lamp, as the cap will likely last longer. The high frequency current limiter will be getting a clean DC at all times, and so the only flicker I'd expect at this point will be from this high frequency regulator. The video did not put a 'scope on the chopper, so we don't know the frequency.
I've bought some suck-it-and-see parts: a small selection of LED lamps, and a couple of DC-output 'transformers', and a bag of Wago 224-112 connectors and Wago Light enclosures, in case there's going to be a bunch of wiring. I'll test the lamps against the in-situ 50w AC 'transformers', and compare the results against the new DC ones.