Take a look at this link:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC114026/
Its not new tech, its not even that complicated. Fortunately only done with a mouse virus.
0% mortality to 100% mortality from one gene insertion. We dont need to know everything to find one dangerous gene..Even high mortality in attenuated virus pre-immune which is a very potent form of vaccine.
The problem is not making something lethal, its making it lethal and secure that the host survive long enough to pass on the infection. The reason why bird flu still scares officials so much is that its highly lethal (but below 50%) and sufficiently contageous to spread, but it cannot approach 100% mortality while doing that.
I really dont think we should find a solution to that problem.