[dvgrn]

It's a bit hard to see how this RCT trick could be useful for reducing anything besides the number of gliders.

RCT is basically one very unreasonable end of a wide spectrum: you can use a very small number of gliders to build something, as long as you're content to have the construction take a ridiculously long time. Conversely, you can build that same thing in a lot less time, but it will take a lot more gliders.

[geysersam]

Also, even if the maximum number of gliders is fixed (15), that does not imply any limit on the amount of information needed to store their positions.

The glider positions might very well require more storage than the desired pattern itself.

[dvgrn]

That's definitely completely true. We can specify the relative positions of the initial gliders at each of the three corners of the RCT pattern in just a few dozen bytes.

But the number that says how far apart those corners are from each other has very roughly half a million digits. The exact number depends on exactly what pattern is being encoded by the RCT pattern -- I think the example construction of Alan Hensel's decimal counter pattern needs somewhere around a 450,000-digit number.

There are some optimizations underway to decrease that number by a few percentage points, but it's always going to be a very big number!