Nobody knows how likely these two new viruses are to launch a pandemic. Nor will we know soon, unless the news is very bad. We weren't able to observe the precursors of previous pandemics, so we don't know how long pandemic viruses "typically" hang around before they acquire the ability to spread efficiently from human to human.
If H7N9 or MERS-CoV ("Middle East Respiratory Syndrome Coronavirus")does go pandemic, nobody knows how bad the pandemic will be. The swine flu (H1N1) pandemic of 2009-2010 was very mild. So far, H7N9 and MERS-CoV have horrifically high case fatality rates. Will these viruses become less deadly in the process of becoming more contagious? Nobody knows.
While both the probability and the magnitude of these two new risks are unknowable, most experts would guesstimate them as far from negligible. Most experts share your judgment that a severe pandemic isn’t vanishingly unlikely.
Pandemic preparedness therefore makes sense, on an individual and a societal level.
One thing we do know with near-certainty. If there is a pandemic, we will face its first wave with very little pharmaceutical help. Antivirals will be in short supply. And vaccines will be nonexistent. No one has ever created an effective vaccine against any human coronavirus. Flu vaccines of modest effectiveness are feasible, and work is proceeding to develop an H7N9 vaccine. But so far there are no plans to mass-manufacture the vaccine until it's clear that a pandemic is imminent. So wealthy countries can expect usable supplies perhaps a year or so into the pandemic; developing countries probably can't expect usable supplies ever.
So real pandemic preparedness means non-pharmaceutical preparedness -- from stockpiling masks to cross-training people in essential job skills to figuring out ways to diminish the need to go into crowded places while a pandemic wave is locally intense.
I am not an emerging infectious diseases expert. I'm a risk communication expert. And in recent weeks I have been amazed at how seldom public health officials have urged individual, family, neighborhood, community, and business non-pharmaceutical pandemic preparedness. (For an essay on how U.S. health officials are ignoring non-pharmaceutical pandemic preparedness, see http://www.psandman.com/col/H7N9-2.htm.)
Health officials have been admirably candid (for the most part) about the risk of an H7N9 or MERS-CoV pandemic. But they have far too often implied that they have our backs so we don't need to worry. Even in the wealthiest developed countries, that's a myth. In less wealthy developing countries it's almost a fraud.
I hope development planners take your excellent blog post to heart!