> One day, scientists might be able to successfully mimic the expansion of the interstitial space that does the mental janitorial work so that we can achieve maximally efficient round-the-clock brain trash pickup.

We can ask the same question the article poses initially about why we still sleep. Why hasn't this evolved yet? What are the disadvantages of this 'always-GCing' approach? In a best-case scenario, it might just be some sort of historical limitation that no longer applies* (just as our tendency to get fat is a result of an approach to resource conservation that made sense in the ancestral environment, where food was scarce and opportunities to feed intermittent, but does not in modern civilization, where food is nearly always available). In a less appealing scenario there might be some tradeoff that causes us to think less efficiently when this interstitial space expands.

[*] The extra fluids have to come from somewhere, which would mean they're not available for other tasks. Similarly, digestion is expensive--blood flows to the intestines after a meal, and if this is to happen then (since in the short term, you have a fixed amount of blood) it's less available for fueling your muscles. (And if you force yourself to be active right after a meal there's contention for these finite resources. Ever go for a run right after eating?)

Though perhaps there's less fluid involved here than there is with the intestines.