Today I don't think it is. Personnally I'm still uneasy about floating point representations, but for integer based images practically there is no longer an issue. An aim with which I'm sure most of us would agree. However, this is NOT reality at present, at least not for the quantity and size of images which many scientists produce. From or to the ESRF I think around 10 Mbytes is the practical limit which can be successfully transferred over internet.
Efficient compression is desirable.
I think that I understand the idea, and Brian has now given examples, however I can't see this working in practice. My main aim would be the transfer of raw detector data from acquisition point to analysis software. Yes, the aim is essentially the same as that of the IUCr CIF project. The scale of the problem is completely different. Once data is processed to a list of hkl's and I's, or somethingelse, the quantity of information is enormously reduced from the raw data.