If I would use PCIe 1x Riser Cards with a Motherboard (e.g. 1155 ASUS Z68 or ASRock Extreme 3) and use all PCIe that MoBo is giving me - will the MoBo fuse or burn my house down? The setup will be properly cooled of course. Which MoBo manufacturor is the most solid for these kind of task?
If you are concerned about the 75W drawn per PCIe card from the mobo you can splice into the riser and supply 12V to the card directly.
If you are going to use that many cards I recommend, I haven't done a detailed look but you would be asking the board to potentially pull 350+W just for the PCIe slots, the wires will definitely get toasty as others have found.