This is an interesting question, Visitor...
well, first of all, remember there is a difference between DC - which is a digital (therefore, immaterial) image i.e. information, and a DCD - which is a physical manifestation of that image - on paper it is fixed at A4 size, for convenience and consistency reasons.
a DC image can be made bigger, how big it depends on the image structure. most DC images are composite - made of pixels and vectors. the DC images that are all vector, such as ›this one, can be scaled up to any size, with no loss - they are pure mathematical equations.
other DCs can be scaled up too, but you will start seeing pixels, when more than 3 or 4 times bigger.

note:
most DCs are now all-vector, certainly all ›Versioned Editions (VEs) are...