I have for a while been thinking about this situation of talk back...
One solution could be the use of UHF!
We have a vast network of Internet linked repeaters/access points/nodes sat idle.
We keep talking about use it or lose it.
To expand on this I'm talking about DMR, or maybe one of the other digital voice modes.
Granted it does mean buying another radio, but, the price of these have really come down recently.
With this system we could have a UK wide "room" for talk back, and maybe another "room" for European wide talk back.
You can also call individual radio's for 1 to 1 talk back.
I do admit to having no experience of these systems directly, so I don't know how well it would hold up to high demand, or how we go about creating our own rooms on the network, but this is a minor detail.
The great thing about it is, we are still using radio for talk back, so real time audio and no keyboards or sun glare, but still having the advantages of the Internet.
Also, in most cases a simple handheld radio should be sufficient.
Maybe I've missed a key point here? With this idea, but it is just that, an idea.
73s Gary M1EGI