I'm going to cut rD some slack here. And anyone who's been around here a while knows I rarely cut Disney any slack, lol! But here's why: I am managing communications on COVID-19 for another very touristy area in FL and I can tell you that things are literally changing by the hour here. My job is usually quite calm, relaxed, and I get plenty of notice about things before I need to communicate them - the last 3 days have been nonstop messaging, changing the messaging, adding new messaging, on and on. Our audience is getting frustrated because we keep re-messaging. I think Disney has its hands full dealing with the closure of parks and resorts/restaurants right now. There likely isn't time to deal with a race weekend that isn't on the immediate horizon. Recommendations and mandates at the state and local levels are constantly changing, too, and that impacts WDW and any decisions it makes. Knowing what I know right now about how things look in Florida, I very much doubt the races can go on, but I can see several reasons to delay an official notification.
People who know they won't attend can cancel resort/ticket/dining now without penalty, so no need to wait on rD to make a decision or issue a notice. As far as rD registrations go, whatever will be will be: making your decision now vs. later isn't likely to change anything in that regard.