Do we have free bits in the info pointer itself?

Our heap object header is one word -- an info table pointer https://ghc.haskell.org/trac/ghc/wiki/Commentary/Rts/Storage/HeapObjects. Well, a 64 bit info table pointer leaves *at least* 16 high bits inside the object header for other purposes, right? Is there any problem with using these other than having to mask the info table pointer each time it is dereferenced? Thanks, -Ryan