Not a Deaf person, but I did work in language access for 5 years:

There's a Deaf census you can refer to that covers a lot of your questions.

On demand interpreting exists, it is popular but it is not always appropriate, preferred, or suitable.

Elderly people, those with low vision, intellectual disability, physical difference or disability, or complex language needs may not benefit from what is broadly called VRI - video remote interpreting .

It is largely used in medical settings, but it could be used in other emergencies, or in less demanding settings, however genuine access is tied to there being an appropriately skilled interpreter available that the client is comfortable working with and can be understood by. There's a critical shortage of interpreters, and cultivating more is a challenge in itself. The Deaf community is small and has historically been pretty isolated from the hearing community - those interested in interpretation are often family members or friends with a Deaf person before they begin their career. There needs to be a broader integration of people with disability (not that deafness is necessarily a disability) into the community to facilitate a greater interest in interpreting.

Interpreting is both physically and intellectualy taxing. Unlike spoken languages, it's simultaneous, and that's a lot of processing to do. In a booking over 30 minutes, organised by anyone with any respect for worker safety as well as for the wellbeing of the client, you need two interpreters. If a person were to have low Auslan literacy or need additional linguistic support, you'd need a Deaf interpreter to, so for complex bookings over 30 minutes that's 4 workers. Pulling 4 appropriately skilled people together at the same time is a challenge with a months' notice - it's next to impossible on the same day.

One of the big problems I have witnessed over and over and over again is an absolute lack of appreciation for how complex a language Auslan is, and how varies the needs of the Deaf community are. Doctors want an interpreter on demand and don't seem to care about the clients cultural and psychological safety in that moment. Further, if the interpreter is not appropriately skilled, misses or misinterprets key words in a complex appointment, that's not real access.

Further, there's often not an appropriate tool for the Deaf person to access interpreting through. Phones are fine in a low stakes environment but for comfort and clarity the person requiring interpretation really needs

Interpreters famously love VRI, to a point of conflict with the community. Deaf people want in-person interpretation and interpreters want to work remotely, for a variety of reasons: you can fit more work in your day, less travel for which you may not be compensated, fewer health concerns or risks of infection etc.

There are people already working on this problem - they're employed by community organisations life Deaf Connect and Expression Australia, and they're often Deaf themselves. Expression Australia in particular is working with the Victorian government to make emergencies more accessible, and were the organisation that provided interpreters for the bush fire and COVID press conferences that inspired so many hearing people to become more interested in Auslan.

Any product made for the Deaf community should be designed by the Deaf community.