It's going to have to be the opposite of trial and error, I would think -- though maybe in some sense some of the underlying searches for useful predecessors of patterns like Sir Robin could count as "directed super-high-speed trial and error".
The problem at the moment is that nobody can see how to direct those searches toward a predecessor that's made entirely out of gliders -- it's clear that the Sun will burn out long before a trial-and-error search would be at all likely to return a result.
We can easily make a huge number of non-Sir-Robin predecessor patterns that will evolve into Sir Robin -- and we can find ancestor patterns for most of those predecessors, too -- but each step backward always produces something that's a little bigger, a little blobbier, and a little more random and chaotic looking than Sir Robin was... so ultimately all we're doing is making the problem more difficult with each step.
The problem at the moment is that nobody can see how to direct those searches toward a predecessor that's made entirely out of gliders -- it's clear that the Sun will burn out long before a trial-and-error search would be at all likely to return a result.
We can easily make a huge number of non-Sir-Robin predecessor patterns that will evolve into Sir Robin -- and we can find ancestor patterns for most of those predecessors, too -- but each step backward always produces something that's a little bigger, a little blobbier, and a little more random and chaotic looking than Sir Robin was... so ultimately all we're doing is making the problem more difficult with each step.