Noble goal, but extremely difficult to implement in a economical, global way. Thermodynamics dictate that movement of heat from one area to another causes a cooling of the original heat source. In the big picture, a magma chamber has a huge heat capacity. However the means to extract the heat will focus on small pieces of it - causing excessive local cooling and loss of heat capacity in those areas. Net result is a fairly rapid degradation of the heat transfer capacity of the contact site.

Past technology has focused on heat recovery from geyser fields and vents. A utility company in northern California used to harness the steam and hot water from them to drive turbines to produce electricity (research The Geysers in California - may be defunct now). Iceland already utilizes passive geothermal heat in many, many small ways - lots of houses and buildings incorporate steam heat naturally from ground vents. These are the easy ways.

A larger "industrial" system will require larger heat exchange systems (think plumbing similar to the primary cooling loop in nuclear power plants) constructed well underground in close proximity to the magma chamber. We're talking high temperature alloys here - likely titanium. Generally these types of systems would need to be closed (magma heats up the piping/heat exchange coils that contains fluid used to transport the heat), as capture of heated water in direct contact with the magma/rock will cause transport of dissolved solids - which in turn will deposit in the piping and plug/scale it up.

So yeah - great concept, but harvesting geothermal heat in large scale systems is rife with its own special problems. Iceland is definitely the place to explore it though. Being jaded, I'm assuming this is mostly pandering to the climate change crowd, but it is likely to at least generate some meaningful new technologies. I hope anyway...

This sounds like the plot to a new science fiction movie. You know, one of those that ends in a horrible disaster...