However, it turns out that congratulations were premature.
I was done with work, got all hyped up to start calibrating the printer, then a series of screwups occurred.
First, the Z-rod unthreaded itself out of the coupler (for the umpteeth time).
While messing with the Z-rods, i've whacked them out of the somewhat de-wobbled state and into pretty nasty shakes.
Then the Z-axis got bound, due to me misaligning the left and right side while trying to get the wobbles back under control.
And then i've made a series of tiny, but crucial errors that culminated in self destruction of the hotend.
1. The Gcode i've generated with Slic3r had Cooling enabled, but with first layer cooling turned off.
2. I've set the skirt to 5 perimeters instead of 3.
3. I haven't zeroed the Z axis correctly, so the nozzle ended up squashed against the glass (not all the way, but nearly).
4. The temperature i've set before handing over the control to the Slic3r file was 175, while the temp set in Slic3r was 195.
5. I've had the Z raised to 75mm before starting the print.
All of that conspired to prolong the time before the fan went on AND increased the pressure inside the hotend by a fair amount.
The bit of filament under glass transition was right around the middle of the überthin SS tube and started to swell, eventually blocking the filament.
But that's not all - it swelled enough to DEFORM the tube. That's right, the tube bloated around the middle (where the support is thinnest), with bloated filament in it. End result - deformed tube and stuck filament.
I took it all apart, heated up the SS tube, pulled the filament out when it softened enough to get squeezed back through the tube, then torched the remains of PLA in the tube. I think the hotend's pretty much busted now, because whenever the pressure and temperature in the SS tube rise enough, it's going to happen all over again, except much more easily this time, because the tube's already deformed.
I'll take some post mortem photos tomorrow...