One point made was about the complexity of presenting where there are different information sources, remote presenters and remote students. It can be very difficult to manage this technology when trying to present as well (teachers usually do not get tech assistants).
For those with less complex AV requirements, your webinar system may be sufficient. Universities now routinely offer students the ability to take part in a seminar remotely. For this video-conference system tailored to educational use is provided and usually called a "webinar" system. While intended for remote students, the same system can be used to transmit the presentation to an overflow classroom in the same building or at a remote campus. Students in the main room could use the webinar system to display the presentation on their mobile deice and respond.
One of the devices on display, the "AirBoard", was deceptively simple. This is a document camera which clips onto a whiteboard. There was a fashion for interactive whiteboards, which detect the location of a special pen and convert this to a digital image projected onto the broad. However, these can be hard to use and expensive to buy.
The alternative to a smart-board is a camera which relays what is written on an ordinary white-board with an ordinary marker. This image can then be transmitted to a non-interactive screen and to the student's devices.
One limitation is that the camera has been designed for whiteboards, but ANU mathematicians still like to use blackboards. I have suggested Crestron add a feature to have the camera to work with blackboards.
Another limitation with this camera is that the image processing eliminates the image of the presenter's hand. This has the advantage that the student can see the text uncluttered. But the presenter can't point at what they have written, for emphasis. Perhaps the system could be programmed to recognize a gesture of the presenter pointing and display either their actual hand or a pointer.