You can vary ratio of Pineau to gin to taste. My favorite bartender makes me variations of this; he has used Nolet's, Oola, and Botanist gin, and often finishes the drink with an orange twist and a barspoon of something interesting- he has used Benedictine, Luxardo Maraschino, and Cocchi Americano, all to good effect. Sweeter than a traditional martini, but the gin flavors still shine through.
Why have I not thought of this? I've loved Pineau des Charentes for decades, and it would seem a natural with gin and a barspoon of something. Simple and tasty means an ideal cocktail to me. Thanks Christina, and Rachel!