Possibly as part of type-annotation-spacing, possible as a new rule. Right now, the punctuation that I can think of are | (union), & (intersection), [] (array or tuple), and {} (anonymous object definition).

The obvious preferences I can see for | and & are no-spaces (string|number) and spaces (string | number). Tuples and anonymous types are a bit different -- the two relevant spaces are after [ and before ], but not before [ or after ]. A more real-world-y example might be:

type keyedEntity = baseEntity & { primaryKey: string|number; records: [ number, string ][]; };

This could be formatted a number of different ways.