thank you for opening this discussion. along with larger image sizes and aggregation of data across increasingly large studies, there is a need for:

a. serializable compression and the ability to operate on a single voxel/plane time-series or a single volume of a 4D-volume.
b. extended sequence meta-data derived from different pulse-sequences (for example, multiple echo-times and flip angles for flash scans) that are useful for reconstruction algorithms
c. an extensible schema for neuroimaging data formats that's consistent across conversion from manufacturers own dicom fields

one option that addresses (a,b) is HDF5  (http://www.hdfgroup.org/HDF5/). the MINC2 (link) format uses HDF5 and is a good option to look into as a starting point.

for c, the XCEDE and XNAT schemas are steps in that direction, but we haven't had much buy-in from the community at large. however, with increasing public distribution of large scale studies, it's worthwhile to start considering/extending some of these options seriously.