I truly hope that Gnome and particularly KDE can resist to this change, because of its complete lack of flexibility. If I read correctly:
1) indicators must go to the top right of the screen no possibility to change it.
2) indicators must be in a fixed order, no possibility to change it.
3) once indicators are in place, all applications using the system tray must be modified to work with indicators.
If Gnome and KDE accept this, margin for other distros to take different paths will be minimal and Ubuntu will actually end up imposing its choices on everybody. As a matter of fact they are already doing so by telling developers that they must stop relying on the system tray applets even before Gnome and KDE can take decisions about that.
A first point against the current suggestion for indicators is that on screens that are much wider than tall, to put things both on the top and the bottom of the screen is a very poor design choice. The gnome idea of having two panels, one at the top and one at the bottom of the screen was nice on the 4X3 screens that were used a few years ago, and can be nice today on phone screens that have a vertical form factor, but is not ok for the "panoramic" screens that computers and laptops get today.
Recently I always reconfigure gnome to use a single panel a la KDE, otherwise on 1024X600 screens there is not enough estate to vertically display anything. To have 2 20-pixel thick panels is to steal from applications 7% of your vertical space and screen area.
A second point is that maybe the reason why the "system tray" paradigm has sticked and the "notification area" has not is that people do not want a notification area. Maybe they exactly want a "system tray", namely a single place to quickly check and access system or hardware related applications that typically live for the same amount of time as the session itself. It is not a substitute for minimization nor an inconsistent way to hide windows: such applications are not started as a window and then actively minimized or hidden. They start automatically and readily in the system tray form, something that is completely different from the very start. And no... the possibility to conceal things in the tray is not like "masking tape so you can cover up unwanted warning lights". It is much more like the toolbox paradigm. Ideally one would like to have a toolbox with an infinitely wide opening, so that when you open it you can see all the tools. But the opening is limited in size, so what do you do? You put the tools that you use less on the bottom of the toolbox, so the ones you use more can be visible at the top.
Finally note that the main argument that ubuntu makes against the system tray is that programmers have too much freedom to make the many applets inconsistent. Unfortunately, by the same lines one could say that the desktop must go because programmers have too much freedom to make the many applications inconsistent.