It should be possible to navigate 7xx related entries tracings via searches on standard numbers, rather than being limited to just textual or control number searches.
For me is not a good idea. ISSN are quite valid as persistent identifiers but ISBN not. ISBN are valid identifers for Book avaible fom publishers but not after the edition is not more avaible. Publishers can reuse them. So ISBN are good persistent id for booksellers but not for libraraies.
I suggest this be optional, enabled by a syspref (UseStandardNumbers). I know that ISBNs are neither persistent nor guaranteed unique, but in any given collection, they are likely to be close enough for the purposes of linking records. This provides a reasonably reliable link in libraries that use linking fields extensively in their existing data. This feature is not going to make it into 3.4.