[jcrawfordor]

The ATC scenario has significantly more relaxed requirements than ILS, and this change is intended primarily to provide coverage in situations where there is no, or limited, coverage from conventional methods (primary/secondary radar), and likely ultimately to replace the outdated secondary radar system with a space-based one.

ADS-B is not a guidance tool and will not lead to any more usage of GPS for guidance than is currently common - and certainly won't impact ILS. They're just totally different use-cases.