There are two reasons why plasma will remain a niche player. These are scalability and reliability.
Scalability by itself will relegate plasma to a niche market. The first scalability issues is that there is a finite limit to which plasma cells can be shrunk. This directly limits the resolution of any given panel size produced. The second scalability issue is that the display substrate is the display screen. Thus larger display screens, require larger plasma panels. The manufacturing ability and yields drop off dramitically beyond the panel sizes that are produced today. To make matters worse for plasma, neither of these scalability issues apply to reflective LCD technology (LCOS, DILA) and apply only marginally to transmisive LCD and DLP. Plasma will contine to do well for small panels, and may compete with LCD panels for handheld panel displays. In order for handheld plasma screens to compete with LCD, the power consumption issues in plasma must be addressed, and that is unlikely to happen with an ionized gas that must be excited.
The reliability of large glass panels, incorporating ionized gas cells that consume large quantities of power (relative to other displays), is far lower than a small reflective LCD panel that consumes almost no power. Plasma panels are susceptible to shock, aging and atmospheric pressure (or lack of it).
The scalability and reliability reasons is why LCOS will eventually pervail. Reflective LCD panles place the control electronics behind the actual pixel cells, thus the cells can contine to be shrunk without regard for the controls for each cell. Where as transmissive LCD panels must incorporate some of the control circuitry into the light path. This limits the ability to shrink and scale each pixel, and thus the transmissive LCD panels themselves. DLP will also suffer from scalability and reliability issues once a certain pixel density and size is reached.
None of the above is new news. Some basic reading on display technologies will yield all that and a lot more.
Where it gets real interesting, is who can produce what, and when, at what cost, and with what features. Today 50" plasma panels, despite their obvious performance issues, have a market with their light output and wide viewing angle. Tomorrow that performance gap will be reversed, and the price will end its use for panels of any real size.
Light engines that will enable very narrow LCOS, LCD and DLP display devices are already on design tables. Plasma needs to be credited for highlighting the consumers need/desire for unobtrusive display devices. We can love plasma for what it represents in product features, but it would be a mistake to assume that it is the technology that will continue to deliver on the consumers needs/requirements/desires.