I/M/O, Detwiler gets the Ellsbury deal done without anything added. They are a little too left-handed in their rotation with Lester and Doubront (and maybe Morales), so it isn't ideal, but that is the right talent level.
They originally drafted Meyer before he went to college but could not close a deal. Meyer is a lot, and they could use a fig-leaf player to go onto their roster. They have some minor league SS/3B depth, so perhaps Morse and Meyer for Ellsbury and a SS in their system not named Bogaerts. I am not too keen on putting Meyer in a deal, but I don't know what righty plus Morse in the Nats system would get the deal done.
They have a hole at first. With JB Jr. and Bryce Brentz, I'd imagine that Morse would be interesting to them as a righty to play first for a few years with an extension, maybe more than committing to Cody Ross.