Over the past couple of months I've socialized this idea and got some very interesting feedback from friends and family and now think that ROE should supercede ROI in much the same way as the guys at Redefining Progress have argued that Genuine Progress Indicator (GPI) should supercede GDP as a more accurate measure of economic and social progress -

GPI starts with the same accounting framework as the GDP, but then makes some crucial distinctions: It adds in the economic contributions of household and volunteer work, but subtracts factors such as crime, pollution, and family breakdown.

ROE needs to take account of the resources consumed both creating and running IT infrastructure; whether these resources are renewable; the cost associated with extracting/acquiring these resources and so on.

In other words the ROE of a complex entity such as a next generation data center (NGDC) will itself be complex and will therefore need to be decomposed into its constituent parts (interestingly in much the same way that the management of such an entity needs to be unpacked) with the overall ROE a function of the constituent ROEs.

Given that ROE typically needs to be computed over the lifetime of a long running entity such as an NGDC we need to find a way of expressing its net present value (NPV) in the same way that we compute the NPV of a cashflow for a complex financial instrument such as bond with embedded optionality, where the latter represents, for example, a specific technology refresh. In place of interest rates there will be a set of forward rates for resources based on their projected scarcity/impact on the environment and so. Thus the NPV is itself a measure of the sustainability of the long running entity.

This link between ROE and sustainability is fundamental. Redefining Progress recognize this in their mission statement which is to work with a broad array of partners to shift the [US] economy and public policy towards sustainability.

Perhaps Redefining Progress are the right organization to take this concept forward? Their Chair Claude Poncelet was formerly in charge of Environmental Policy at Pacific Gas & Electric who are themselves taking a leadership role with their energy efficiency programs.
Footnote
Out of curiosity I googled "What is Progress" just before posting this article. I was amazed by what I found. Ever wondered what John McCarthy does in his spare time? Take a look - you'll be surprised!