Thanks to the input from Joris and others various enhancements from the BigTiff proposal are now part of LibTiff. Hopefully it will soon get the blessings from Adobe, who own the Tiff Standard and become part of the official Tiff spec and encourage wider adoption.
Adobe seems to be aware of the issue with the 4Gb Tiff barrier and looking into already implemented enhancements such as by Aperio. John Nack points to it in his Adobe Blog. Hopefully Photoshop will soon take this up and implement a tiling scheme for images bigger than 30kx30k pixels.
Meanwhile I am busy shuffling BigTiff into my processing stack. Testing it with Gdal(Support works fines) and Ossim(Support not yet stable). If anyone wants to help in the testing with other applications grab some sample images here.