So I did a few differential footprint tests, in order to discover that each VarHandle instance references its own MethodType[] array.

It might be advisable to explode the MethodType[] array into the individual fields. MethodType-s are cached already in MethodType.methodType factory.

***** double (static):
 footprint:
     COUNT AVG SUM DESCRIPTION
         1 32 32 [Ljava.lang.invoke.MethodType;
         1 32 32
java.lang.invoke.VarHandleDoubles$FieldStaticReadWrite
         2 64 (total)


java.lang.invoke.VarHandleDoubles.FieldInstanceReadWrite object internals:
 OFFSET SIZE TYPE DESCRIPTION VALUE
      0 4 (object header) N/A
      4 4 (object header) N/A
      8 4 (object header) N/A
     12 4 MethodType[] VarHandle.types N/A
     16 4 VarForm VarHandle.vform N/A
     20 4 (alignment/padding gap) N/A
     24 8 long FieldInstanceReadOnly.fieldOffset N/A
Instance size: 32 bytes (reported by Instrumentation API)
Space losses: 4 bytes internal + 0 bytes external = 4 bytes total

Also, since there are four elements in MethodType[], we would reuse the alignment gap @20 without producing more gaps. Back-envelope calculation says that we save 32 (MethodType[]) - 8 (two additional slots for references in VarHandle) bytes per VarHandle instance.