Nepal security assessment
Nepal is a mess but you are safe
The world is a mess, Nepal is also, only currently more so. However, in summary: it is safe to trek and travel in Nepal, there may be strikes, delays and inconveniences—there may not—BUT you have never been a target. You are safe from orchestrated political violence, even Americans, so come have an adventure.
Personal safety
Theft from tourists is very rare and I feel secure travelling with expensive camera gear on our treks.
Kathmandu
Kathmandu is a city on the edge. The air pollution is disgustingly bad and dangerously unhealthy, #177 out of 178 capital cities, the rush hour traffic is to the point of virtual gridlock and the city can't even dispose of its rubbish satisfactorily. Despite these rather big issues, the historic old parts and the tourist ghetto of Thamel still have a chaotic charm.
Air safety
Nepal as only one main international airport (TIA; for a country of nearly 30 million), which is a complete mess with international flights mixing with 18 seater small planes and helicopters. Flights are frequently delayed and the terminals are overloaded.
The safety record of small plane flights is not particularly good, however conditions are incredibly challenging, and flying is still safer than road travel.
US travel advisory
The State Department has simplified their system, here is the Nepal travel advisory.
The future
The problem is and always has been "the fox guarding the hen coop" with the politicians writing the rules to govern themselves, and they cannot see beyond short term political gain. In spite of a revolving door of the same five corrupt and morally bankrupt prime ministers and a destructive rent-seeking government culture, the country is gradually growing with business pushing inexorably forward with a bright spot in hydropower generation for India. The economy is kept alive by remittances from overseas (approximately 10% of the population is working overseas, literally millions of people). Business is growing but not enough as the unemployment rate is horrifying, and wages are barely liveable. Administratively everything is held hostage by high level politicians despite a transition to a federal set up with seven provinces. Even the unbiased International Crisis group says the political parties "are badly run and ideologically impoverished organisations with few policy goals, unclear agendas and chronic leadership crises". Expect occasional disturbances and strikes but normally these don't have too much effect on trekking plans.