I don't think Penske moves the Indy 500 date/time, there's too much tied up in the fan experience and why mess with that? However, I think the locked-in spots are a real possibility. Traditionalists will howl but IndyCar teams are still on shaky financial ground and protecting them for the biggest race does make sense. Qualifying weekends are snoozefests that make very little money.
Nascar will race on the IMS road course, I think it's close to happening even without Penske but with him it's definitely done. That's the easiest thing in the short term to bring back interest. Long-term, it might be night racing.
I think IndyCar/Nascar doubleheaders at other tracks, if not IMS, will happen too. It's time to throw everything on the table.