afuna can correct me if I'm wrong here, but regarding the split function and its missing opposite, I think what may have happened there was that LJ's S2 string class was seriously deficient, so an effort was made to improve the string functions, specifically. In LJ, we constantly bemoaned the way we had to iterate over each character of a string in order to do the simplest string operations, so when the opportunity came to give the string class some useful methods, it was really exciting! I may have wept a little. So possibly, through all the joyful tears, no one noticed that arrays of strings were now missing the natural complement of split.

PS If you want to dole out any other tasks to me, I am more than willing to tackle something.