Correction: A microbiologist pointed out to me that if ebola mutated, the odds it wouldn't be the same virus, i.e. not as virulent because mutation is a randomized process so all variables of the pathogens genetic structure are at play. So if ebola remained virulent and became airborne, it could be reasonably assumed it was weaponized and engineered intentionally.

The coming global economic implosion could make the population weakened due to lack of nutrition which may facilitate spread of disease. Yet that still doesn't explain a potential pandemic. I am still searching for a plausible scenario.