Most people in the UK and Ireland use the UK English layout, which is marginally different from US English. This is a market of ~65m people and therefore not to be dismissed lightly.
This would require the following five alternative keycaps to be manufactured:
[2"] [3£] [’@] [`¬¦] [#~]
These would replace the US-ascii 2, 3, apostrophe, backtick and backslash keys respectively. This is dependent on an “international key” scancode for the backslash keycap, which doesn’t appear on the proposed default Model 01 layout. We may also then require a sixth alternative keycap [|], depending on the position chosen for the international key (which will determine whether we can reuse the us-ascii backslash keycap).