I see that in safe-money package they choose the following approach for having aeson instances and other: they introduce flags in .cabal file and depend on each library conditionally. I think we can do the same thing:

• https://github.com/k0001/safe-money/blob/master/safe-money.cabal

Not sure we want all instances, but I think it's worth to have the following ones:

• Hashable (hashable)
• NFData (deepseq)
• ToJSON/FromJSON/ToJSONKey/FromJSON/Key (aeson, also maybe with one extra newtype for additional behavior with mcs suffixes and without)
• serialise (I saw this library was used in different projects)