We do not show selections in layouts because selections in 9 are temporary, whereas in 8 they were persistent.
We can show selections kept per-session, but we are not sure that's the right way to go. Let's say we show selected objects in layout frames. So, if you open a MAP file and then open a layout for a drawing, it shows no selected objects at first, but if you then open the drawing and select something, the layout does show selected objects, and if you then close and reopen the MAP file, the selection is lost and the layout shows no selected objects again. That already feels brittle, what the layout shows seems unstable, but what's next is even worse. What about allowing to restrict a layout frame to show only a subset of the objects - should we allow restricting the extent to the selection? That's what we were allowing in 8, so there're perhaps natural expectations that 9 should do the same, but with selections being temporary is that really the right approach? The layout frames zoomed to the selection are going to reset all the time, is that really what we want? We think it is better to concentrate on specific things you were using selections for and to make those things simpler if they are too complex now. For the general case, everything you could do in 8 with selections, you can do in 9 with saved selections, which are just ordinary boolean fields.