Nice idea, especially for people who would rather not roleplay the bookkeeping aspect.
Writing coordinates down on an piece of paper, or just remembering where the mutated molerats are, is something that makes a game "inaccessible", pandering to masochistic "Olde Skoole" simulationists.
Every character is assumed to have a non-lootable "PIPBOY", which presumably would have the ability to add map notes.
So the suggestion should be implemented.