This depends entirely on the population. Rare individuals with unique DNA markers are easier to re-ID than individuals with more common DNA markers.
But also consider that ethnicity is relatively easy to get from genetic data. So individuals with unique ethnic combinations can be trivial to identify by their genetic data. Now consider that genetic data can also be used to predict traits such as height, hair color, eye color, etc [0].
Reliable triangulation is already possible, and becomes increasingly more accurate as more data becomes available.
But also consider that ethnicity is relatively easy to get from genetic data. So individuals with unique ethnic combinations can be trivial to identify by their genetic data. Now consider that genetic data can also be used to predict traits such as height, hair color, eye color, etc [0].
Reliable triangulation is already possible, and becomes increasingly more accurate as more data becomes available.
0: E.g.this company- https://snapshot.parabon-nanolabs.com/