I'd just like the point out that Elite was procedurally generated for the express purpose of using less ram.
Elite could discard and recreate game areas at will. And there was at most one area (star system) in play at a time.
Starbound, on the other hand, needs to keep track of deltas to its game areas.
Let's talk about Terraria for a minute.
Consider a hypothetical Terraria map made of 'chunks' that are generated on the fly. Over the course of a game, many of these chunks will need to be altered. Plants grow and die, water and lava flood downward, the Corruption and Hallowed spread, new ores are placed, certain mobs place blocks... and then there are all of the player-caused changes.
These changes need to persist. So they would need to be recorded and attached to each chunk somehow.
In addition, the natural effects I mentioned happen map-wide in ways that cannot be predicted prior to generation of each and every map chunk.
On-the-fly, as-needed generation can't work for Terraria's maps. I predict that it won't work for Starbound's maps either.
Edit:
we asked for and did get a month-early release for Terraria (and look how that turned out!).
Wasn't it released early because of a leaked beta that was being extensively pirated? That's what I recall anyway.