I'm an active creator of one-command contraptions, so I noticed pretty quickly after after opening up the new snapshot 15w41b that there was a major problem. When I placed a command block and plugged in the command to generate the mod, all that was summoned in was a single MinecartCommandBlock. It turns out that Mojang has deleted the Riding tag and replaced it with the Passengers tag, so the process of contraption generation is going to have to reverse. Over the next four hours, I built a new command combining template; that done, I'd like to share it with the rest of you Minecraftians.

Blue text denotes a comment.
Red text is stuff you'll need to change.

/summon FallingSand ~ ~1 ~ {Block:stone,Time:1,Passengers:[{id:FallingSand,Block:redstone_block,Time:1,Passengers:[{id:FallingSand,Block:activator_rail,Time:1,Passengers:[{id:MinecartCommandBlock,Command:Tier 1 - set scoreboard stuff and turn off commandBlockOutput,Passengers:[{id:MinecartCommandBlock,Command:gamerule commandBlockOutput false},{id:MinecartCommandBlock,Command:scoreboard objectives add OBJECTIVE TYPE},{id:MinecartCommandBlock,Command:scoreboard teams add TEAM},{id:MinecartCommandBlock,Command:Tier 2 - build the box and fill it with command blocks,Passengers:[{id:MinecartCommandBlock,Command:fill ~2 ~-2 ~-2 ~X+3 ~Y-1 ~1 MATERIAL1 # hollow,Passengers:[{id:MinecartCommandBlock,Command:fill ~2 ~-1 ~-2 ~X+3 ~Y-2 ~1 MATERIAL2 # replace MATERIAL1 #},{id:MinecartCommandBlock,Command:setblock ~1 ~1 ~ wall_sign 4 replace {Text1:"Text1",Text2:"Text2",Text4:"Power to Remove"}},{id:MinecartCommandBlock,Command:setblock ~2 ~ ~ command_block 0 replace {Command:"/fill ~-1 ~-3 ~-2 ~X+2 ~Y-1 ~1 air"}},{id:MinecartCommandBlock,Command:fill ~2 ~-3 ~-2 ~X+3 ~Y-1 ~1 repeating_command_block 0 keep {auto:1}},{id:MinecartCommandBlock,Command:Tier 3 - use blockdata to put the commands into the repeating command blocks,Passengers:[{id:MinecartCommandBlock,Command:blockdata ~3 ~-1 ~-1 {Command:Front bottom left, first to activate each tick}},{id:MinecartCommandBlock,Command:blockdata ~X+2 ~Y-2 ~ {Command:Back top right, last to activate each tick}},{id:MinecartCommandBlock,Command:Tier 4 - clean up the mess of minecarts and the first command block,Passengers:[{id:MinecartCommandBlock,Command:setblock ~ ~ ~1 command_block 0 replace {Command:fill ~ ~-3 ~-1 ~ ~ ~ air}},{id:MinecartCommandBlock,Command:setblock ~ ~-1 ~1 redstone_block,Passengers:[{id:MinecartCommandBlock,Command:kill @e[type=MinecartCommandBlock,r=1]}]}]}]}]}]}]}]}]}]}

Hopefully this helps!