The 512x512 metacell has crept up fairly high on my priority list now, partly because of golfing down the QfT pattern, and partly because I'm curious to see how Golly will handle something like a meta-metacell.
The most recent work on the metacell is still from last September --
http://conwaylife.com/forums/viewtopic.php?f=2&t=2865&p=51287#p51330
-- and probably I won't start the next stage of construction until after mid-April.