The NPS says that the Wildcat Trailhead will be closed on 4/19 due to a prescribed burn in the area. They don't say when it will reopen - but I imagine it will take at LEAST 2 weeks (having previous BLM firefighter experience in St. George) to have it at "100% contained" and having it reopened.
They did NOT mention if you can park somewhere else and still do the subway. Hopefully they will post more information on this soon.