One English expression I particularly like is "for all I know". It has such a level of arbitrariness to it that is unlike any other German expression that is similar to it:
For all I know, every user on GLU besides me is a dog.
There are some good answers over on ELU about that topic that put it into a bit more context.
I could use
Soweit ich weiß...
but this is more like "as far as I know" which is quite different. Because, of course, most users of GLU probably aren't dogs and I know it.
Or maybe something along the lines of
Es könnte genauso gut ... sein.
I don't know. Is there something better that captures the nuances of the original?