To summarize, I see two major paths:
a) Make installer launcher more visible:
b) Use a proxy window asking which use case is relevant for you:
Both approaches are fine in my view and certainly improve the current state. The
implementation of each approach can very a lot, especially for the first one.
One more comment to "we want to provide the default experience":
Gnome Shell is quite intuitive *once you know it*. But if you see it for the first time,
it is not, it brings a lot of new concepts. And it lacks any options to make an important
launcher really visible. For this reason the stock/default experience is not suitable for
the LiveCD installer use case. It is not a fault, because it targets something else. We
just need to adjust it accordingly in this case.