The 2GB model has enough RAM to run the sBitx software comfortably, and to run some other applications alongside it like WSJT-X. Right now, the main time when having more RAM would be an advantage is if you want to create your own builds of the sBitx software; the development software will run better with more RAM. Aside from that, there is no compelling reason to swap the Pis.
My DE has a 4GB Pi because that's what I had on hand when I ordered it. (I bought the basic version and supplied my own Pi and display.) I'm not planning to buy the v2 (I got the opportunity to get an mcHF to use as my field rig instead; the DE will stay in the shack), but if I did I would just leave the 2GB Pi inside.