I keep reading that the ISS might be nearing the end of its life in 5-10 years. Other than the shifting tides of political support, what is the technical limiting factor that would limit the life of the ISS?
Potentially many, and not easily identified.
The original requirement for Space Station Freedom was a design lifetime of 30 years. That was reduced to 15 years for ISS, to reduce development costs. And all that really means is that all the individual components of ISS need to be able to last at least 15 years in the orbital environment, and that the system (as a combination of individual components) also needs to last 15 years.
Complicating factors include:
1) ISS has not been assembled all at once, so for some components the "clock" started earlier than for others.
2) Ground storage has some effect on component lifetime, but the effects will differ component-to-component.
3) Russian standards for design lifetime may differ from those used by the US segment. Many components of the Russian segment are reportedly unmodified from those used on Mir, which had a design lifetime of five years (but wound up lasting fifteen).
Bottom line is that 2013 marks the 15th anniversary of ISS first element launch and beyond that point components will begin to exceed their design lifetimes. That does not mean those components will immediately fail, because there is always a factor of safety designed in. However, it does mean that the component failure rate will gradually start growing after that point and the station will become progressively more expensive to maintain.