This is awesome. I always wondered why KDE took so much longer to start than other desktops, and I'm really glad it's being improved. I've been quite happy with KDE for a while, but if there was one thing I disliked, it was how long it took to log in. The new system is definitely a ton faster. I'm really looking forward to using it in the future.
But the problem is, why does KDE start slower than say Gnome in the first place? It's a welcome addition but why was KDE plagued by this issue for these many years in the first place?
No ones touched the code in years, as Aaron Seigo said on his blog (link on his blog a couple comments below yours, search for "startactive" and its his comment). It was "Good enough" and worked well enough and stable and relative bug free so people said "Dont touch it!" But now people are going back and saying "well yeah, its been 'good enough'...but can we do better?" and the answer is yes, and the work is being done.