Stir together yeast, wine, honey, and warm water in a large bowl. Stir in 1 cup flour (mixture will be lumpy). Cover bowl with plastic wrap and let rise in draft-free place about 40 minutes, until doubled in size.
Add 1/4 cup olive oil, 1 1/2 cups flour, and salt and stir until a sticky dough forms. Knead dough on a floured work surface, gradually adding up to 1/2 cup more flour if necessary to keep dough from sticking, until dough is smooth and elastic but still soft, 8 to 10 minutes (I prefer doing this by hand, instead of in a mixer). Place dough in an oiled bowl, cover with plastic wrap and let rise an hour, until doubled in size.
Turn out dough onto a lightly floured work surface and knead a moment. Cut dough in half and roll out 1 piece of dough (keeping remaining piece covered) to a rectangle 9 x 13-inches. Transfer dough to a lightly oiled 9 x 13-inch pan and sprinkle with half of grapes and sugar. Roll out second piece of dough to same size and cover grapes. Spread remaining grapes on top of dough and gently press in. Sprinkle with sugar and cover with a tea towel to rest 30 minutes.
Preheat oven to 400F (200C) and bake focaccia until richly golden, about 40 minutes. While still warm, brush with remaining 2 Tbsp olive oil.