A PersistenVector that has <=32 elements and is seq'ed will return an IndexedSeq. Though IndexedSeq always fails the chunked-seq? check.
This means a:
is about 4x slower than a map over a vector with 33 elements.
1. Return a ChunkedCons with the "rest" set to nil in PersistentVector.seq()
2. Implement IChunkedSeq for IndexedSeq:
I think option #2 is better since IndexedSeq is used quite a bunch throughout the code base, so the chunking will also kick in for many other code paths.