That would be fantastic, but it seems like MASN is controlling local streaming.
Assuming there isn't a specific exception for the Nats and MASN, MLB is the one controlling it. MASN just hasn't chose to pay the price to lease those rights from mlb to provide in market streaming.
To further the too good to be true scenario.... If MLB gives these rights to all the teams to do what they want, the Nats could choose a very customer friendly accessible option to sell it to Amazon to stream for free or free to Prime members. A lot of clubs wouldn't go in that direction because they value their relationship with their broadcast partner, and that would definitely hurt them. But I have to think the Nats wouldn't have that motivation at all, and would be happy sticking it to MASN.