Thanks Pauan. Regarding lib/re.arc, my take is that if Arc 3.1 does it by default, arc/nu should do the same to match Arc 3.1's out-of-the-box functionality, unless of course if you have specific reasons that justify not loading it up front.
I hadn't tried regex support in Arc earlier so I just figured Arc 3.1 must have it. However, I checked and found that Anarki does have lib/re.arc loaded by default.