The Tern front block is different from the Brompton one.

But the Bike Friday and Tyrell one are exactly the same and meant to use a Brompton front block.

The 3 titanium Birdy versions are completely different bike, they share nothing with the aluminum Birdy and also are different from each other.

Some could argue that these were produced in a very small amount and not available to the mainstream public.

But the New Birdy Classic which is produced by Pacific Cycles only is also a different design and is a mainstream product. There is also the new eBirdy from Pacific Cycles only.

So, I do not think that Pacific Cycles cannot make modifications to the Birdy.

The low rider and front bag are different things used mainly for different purposes: the low rider is more meant for travel while the front bag is in first instance meant for daily use, commuting...