Yes, look for "Deligne's exceptional series". There are no theorems, but several beautiful conjectures.
See, for a start, Le série exceptionnelle de groupes de Lie - Deligne P. - C. R. Acad. Sci. Paris Sér. I Math. 322 (1996), no. 4, 321–326. - MR1378507, and follow citations forwards and backwards!