Shetland as a central North Sea base

What changes if British Shetland lies in the middle of the North Sea?

It becomes a powerful but fiercely contested air and naval base, altering North Sea operations and the Norwegian campaign.

The islands would sit astride German and British movements rather than on the edge of the theater. Britain would build major airfields there, extending fighter coverage and reconnaissance across the North Sea. Those aircraft could influence the Norwegian campaign and intercept operations that historically crossed a wider gap. The same value would make the islands a constant objective for German attack and a demanding position to defend.