This could be amazing.
Saw this in aliexpress. Cant post link, its called (Titanium TC4 Folding Bicycle Frame + Rear Triangel Fork Glossy / Matte Surface for 406mm 20" Bike Wheel
)

I am not sure about the benefit of a 20"/ETRTO406 Brompton vs. its original ETRTO349 wheels.

If it is to only being able to use relatively narrow tires 28mm or 32mm max) it won't improve the comfort nor the performances (I have a Birdy with 3 wheel sizes, ETRTO355, ETRTO349 and ETRTO406 and there is no real difference in performances with the same tires). What would increase the comfort and performances on bad roads is having wide balloon tires like the 50mm Big Apple or 55mm Big Ben. But using 50x406 or 55x406 wheels would increase the total wheel diameter a lot (57mm for the wheel size increase + 30 or 40mm for the tire width increase).

But increasing the wheel size of the Brompton increases significantly its folded size (which isn't the case with the Birdy because on the Brompton, the rear wheel folds under the frame while on the Birdy the rear wheel folds beside the main frame) and the major strong point of the Brompton is its small folded size which is lost when increasing the wheel size.

Titanium TC4 Folding Bicycle Frame + Rear Triangel Fork Glossy / Matte Surface for 406mm 20" Bike Wheel

i do find the brompton design attractive, also the possibility of getting it to 8-9kg with a great fold and good enough ride. Maybe one day when birdy makes a good looking one, I will consider it for sure.

A full titanium Brompton with the same 349 wheels at ~8-9 kg would be nice.

But it might cost 2x what it does now :-/

3sixty has a 9kg half ti-bromp clone for $1700usd. The demand is probably making these clones very interesting.

Snce they're just Brompton clones, 3sixty doesn't sell in the West, and won't ship.

3sixty.kr

A 20" bromp improved clone overcomes several problems that keep me from the 16" version.

This 20" Ti bromp clone is missing a couple essential things though:
1. Front fork.
2. Paypal payment option.
How to overcome those?

I think they have a front fork in the package. Aliexpress is pretty good with their security, but a virtual card that acts like a debit card can also be helpful, im not sure if paypal has a virtual card feature.
I would wait a little for the design to mature, dealers r even putting a premium on clones in asia. But with the demand comes will and the quality is surprisingly high. With software or food products, things that cannot be QA easily, china lacks way behind, but for mechanical things like bikes, its easier for these factories to excel.

A 20" clone in full titanium and disc brakes actually is available in China. But the asking price is a little eye watering at US$3500/- before shipping and taxes.