Lumberyard is a forked version of CryEngine, which Star Citzen was already using (fairly heavily modified for 64 bit precision) so the move to Lumberyard wasn't as big as it seems. They do however refactor other systems like items and inventory quite often which seems to be slowing down development although the new versions do seem like improvements.
Scope creep also knows nothing of Chris Roberts at the helm a crowd funding runaway train. At this point it's now suffering from Hubble's law of the expanding universe, rather than scope creep.
I think they are at last at a scope now that makes sense for a full release. They had to build a hundreds strong, multi-location production team before even getting up to full steam. Games with significantly less scope have taken much longer, without hurdles like that.
It's a double edged sword, because open development has been what drove the crowd funding to such incredible heights (they made 2 million in 48 hours this week, for a total funding so far of 167 million). But it is also the reason for so many people being negative about it's development. People get fatigued of it.
