If nobody else would take the position of Gully lord, we could always have something like a succession crisis. I mean, his heir is ineligible due to being a Kingsguard, his bastard son is ineligible on account of, well, being a bastard, and Tybalt is merely a nephew.

All 3 have equal amount of claim to the throne. We could make that a part of the story if the Gully lord remains unfilled.