According to media reports the Australian Freeview consortium proposes to use MPEG-4 video and an MHEG-5 electronic program guide (EPG) for new Australian free to air digital TV transmissions. The use of MPEG-4 has received the most attention as this would require an extra chip in the digital TV tuners (or some upgraded software) over the current MPEG-2 standard (and also government approval). What has received less attention is that the MHEG-5 standard includes a subset of HTML 3.2 slightly modified for TV. This is used for providing the program guide, but can also be used for web-like interactive content, including advertisements.
MHEG-5 is used in the UK and and New Zealand and so seems a reasonable choice for Australia. HTML 3.2 is a very old web standard and would not be a good choice for regular web pages, but is suitable for the limited role it has on a set-top box. MHEG-5 is also used for digital signage.
Unfortunately no technical details of what Freeview propose to do are provided on their web site. Freevie have also chosen not to use the standards they are reported to be proposing other Australians use. The Freeview web site seems to be entirely composed of Flash media and so very difficult to access.
Another issue is if Freview's limited form of interactive TV will be of much interest to an audience now acquiring iPhones, Wiis with web browsers and Google Android phones. It may be that by the time Freeview is available, it will be of no more interest than old fashioned analogue TV.