TIA Portal V12, Go to, Read/write access

I hope you mean the option available to search where a address (variable) is used in a block.You are right.In my TIA V11 is also "Go to-->Read/Write access" is not selectable.I think that may be part of development or it is not necessary to be available.Currently you have option "Go to-->Next Point of Use" or "Go to-->Previous Point of Use" to search a variable within a block.You also can have a global view(read/write points) of global addresses by selecting the address -->Cross reference information.