Could the reversers of a PW4000 on a 777 be deployed in-flight?
A basic requirement of certification is the probability of any single point of failure that causes loss of the airframe (hazard level = catastrophic) must be better than 10 -9, or one in a billion.  A reverser deployment in flight would meet that level of hazard so system design has to meet that probability level.

In the case of Lauda Air, I would have to assume Boeing made a mistake in the system architecture that allowed a one in a billion event to happen "prematurely", and in fact they introduced a design change to get back to the required probability level.  In the case of the 777, or any other airliner, you have to assume the homework was done properly and the architecture meets the requirement until an event indicates otherwise.

Most of the time, gaps in design redundancy turn up during in-service events that are not as nasty, but that set off alarm bells at the OEM as potentially something more serious, and after a long process of analysis of risk and design, changes are implemented in the field by Airworthiness Directive.

It seems cold and calculating, but the whole thing is a numbers game where people with pointy hats with stars and crescents on them work out probabilities, of risk of death basically, using arcane methods like weibull analysis, to decide what to do and how soon to do it when design flaws turn up.  The transportation system couldn't function without it though.

Anyway, it's safe to say the risk of a reverser deployment in flight on a 777 is microscopic, but it's not zero, as nothing is in aviation.