For me wider tires is a required improvement, when the Brompton was designed, 35mm was a wide tire, but its now obsolete.

But ETRTO406 is not really needed, its a drawback if the combination of wider tires and bigger wheels increases too much the folded size, ETRTO406 + 50mm tire mean about 87mm increase in overall wheel diameter which is lot compared to the current 35x349 and will influence both the folded height and folded length with the folding concept of the Brompton (plus most probably an increase of the wheelbase).

The test bike seen had G-one tires and the only G-one in ETRTO406 that exists is the G-one Speed 40x406, so not a wide tire (excepted if Brompton asked a special size to Schwalbe like it is the case for several ETRTO349 Schwalbe tires sold by Brompton that aren't part of the official Schwalbe catalog).

For the price of the original Brompton bikes, its not comparable to the clones because first the frame is made in the UK with the price of the British manpower and second because the bikes come with a two year global warranty, seven year frame warranty and the after sale support of a wide network of resellers.