It would allow a synthetic virus to get a foothold in your cells more easily, but our cells don't make Pseudouridine naturally which throws a big wrench in the ability of a virus to copy itself. And without replication you don't have a serious infection.

I would be surprised if viruses using U instead of T didn't already exist. After all, don't all viruses work by doing gene editing in vivo, except just localized to one cell?

EDIT: well, I suppose the question is whether cells of living beings could produce the U required for the viruses. But if not, then a wild virus using U instead of T to bypass our immunity also would not be a threat for that very reason.

I feel a bit proud that humanity healed a baby with this tech before any viruses were constructed/released.

I don't thnk the body has a way of making mRNA with pseudouridine.

It's almost exactly the premise of the movie "I am Legend," But it uses CRISPR instead of a Virus as the delivery mechanism.

It sounds like Spiderman tech.