It is kind of only developed when I have a use for it, right now and for the past few months the only version of minecraft that has any sort of mods is 1.7.2
every other version still has not got mcp modding support, so there is very few mods for it. These guys
https://twitter.com/mcp_team/lists/mcp-teamwere meant to be getting a 1.7.9 version done, but they spend more twitting about other shit than letting the minecraft devlopment community wtf is going on with the mcp pack.
Therefore less motivation for me to even want to update it myself.
I do plan to put out an update for 1.7.9 and hopefully it will be easier to add future modpacks and version after that.