I haven't heard it said anywhere yet but I have to assume the reason we're seeing all these new blocks - particularly weapons - in MP but not R&D is because PvP is going to be the major focus in the near future. I can't say I'm surprised since every nearly every other sandbox game has went down the same path. Its a stark truth that no matter how much the community wants co-op first, its PvP that will cause the masses to line a developer's pockets. At least we can expect to see MP bugs exposed sooner rather than later. However, I really think it would make sense to have the new blocks added to R&D and creative as well. Those who are on the regular unstable branch and have no interest in limited multiplayer shouldn't be left out in the cold. At the very least it seems worthwhile to have new blocks also being tested w/o the added lag and other variables introduced by MP.