Shardblade Sharpness Limits?

[SturmOgre]

     Now that aluminium is being used as a defence against Shardblades, I'm wondering how sharp living Blades can get. Given that Shardblades don't really have to worry about structural integrity in the same way as normal blades, they should be able to get pretty sharp. In the modern world, we already have atomically sharp blades that would cut through almost anything like butter if not for their edges dulling too quickly. If a Shardblade could get to that sharpness, it would be basically unaffected by aluminium, at least in regards to cutting power.

But would that be possible? Are there WOB's on the limits of sprenblade shapeshifting?