MLB sets the standards for security, not the Nats, so there might not be much wiggle room there, but they could dedicate a "clear bags" lane just like the Express/No Bags lane and encourage everyone to use a small see-thru bag if they plan to bring a bag. 2016's playoff traffic was a crapshow because of Safe Track and the Metro being shut down, which caused a lot more people to drive. Since Safe Track is over and Metro runs til 1 am on the weekends, this will solve itself for most of the NLDS, assuming we get to be the home team for Games 1 and 2. There would only be one weeknight home game then, Game 5, which might not even be needed.
Busses to RFK would be good. I hope that DDOT did some good traffic pattern analysis last year and learned some ways to improve. Completely closing the side streets might be a good move, because those side streets become a rabbit's warren of traffic and contribute to the flow problems on the main roads (blocked intersections, people trying to merge/turn in, etc).
Port-a-potties on the concourse is just trading one problem (long bathroom lines) for another (even more crowding on the concourses when you decrease the amount of space that people can stand/walk while simultaneously introducing a new place for a queue to form).
"Express" concession stations--- carts with only a small selection of items for cash-only sale-- can be placed around the ballpark to get people out of the main lines and back to their seats quickly. If they're smart, they'll have the items all be even dollar amounts (even better if it's multiples of $5) so the staff doesn't have to make change.
The ability to get a big chunk of the fan base to the park a few hours early is going to really depend on the timing of the games. People will leave work an hour or two early, but it's a lot harder to justify taking a day off. Encouraging them to linger after the game would help traffic but is a lot harder, especially if there's a loss. They could do something in the streetside event space (like where they did Taste of the World) but there may be agreements with the ANC that preclude post-game activities in the first place.
Maybe I'm old and n(d)umb but when I attend any event with 40,000 people, I get there early. I expect delays. I don't carry bags ...
occasionally I have rain gear. I don't buy food. I may have a beer or two during the game. I have a bathroom that's usually pretty open but ya gotta walk to find it. I don't normally drive to the stadium. I walk to Capitol South and take a direct line to my part of NoVA. I expect a trip to the stadium to be a 6 to 8 hour event.
My son got me a motorcycle () calendar some years ago and there was a picture of a guy riding a bike in the rain. The caption: "If you want all the comforts of home, stay there."
^^ This.
Maybe not every word of it-- have more than two beers and buy a big ol half smoke if you want. But fans need to set their expectations properly and not get bent out of shape when stuff takes longer than they're used to. There *will* be traffic, there *will* be lines, things *will* go wrong, but you'll have a better time if you keep your cool.