Fair enough that it's only a fix for this specific case, but that's better than having a problem in that case instead
I do use mostly boxes. Sometimes cylinders as well, and maybe general meshes someday, but we can model a lot with boxes and cylinders (and the occasional sphere for fun). And then of course the ground plane to hold them up. Or ground box as the case may be, but I'd prefer not to have to consider things falling off the side, and I would think a single plane could be faster than a box as well. Considering this is the primary support surface generating the majority of object interactions over time, that performance
could have an impact, but I haven't explored that aspect.
One concern with running a shorter step time is that when something "interesting" happens in the simulation, all of a sudden those high frequency steps can get expensive and cause everything to stutter or fall behind.
Another point: the main issue with small objects (that I've seen so far) is really an issue with high gravity acceleration relative to the size of the object. There may still be other issues, but a gravitational issue is going to primarily show up with support surfaces, and btStaticPlaneShape is really mainly useful as a primary support surface. So in other words, fixing this may be a special case, but it directly addresses a root problem... other inter-object interactions are roughly gravity-neutral, and would otherwise be fine with the longer simulation step.
Our target platform is desktop PCs, across a range of performance levels (notably netbooks unfortunately). We run robots and simulations thereof, and some of the robots themselves are controlled by netbooks, and in classrooms they might not have additional PC resources, so they wind up developing and testing in simulation on the same netbook that later controls the robot... for these robots, 5 cm is quite large -- that's already an obstacle to be avoided. The interesting stuff it can pick up or manipulate is on the order of a couple cm, like chess pieces:
http://chiara-robot.org/Challenge/
So it's pretty debilitating to write off everything under 5 cm as being "too small", because that's all of the interesting stuff. Bullet is really close to handling this, we just need to handle one more order of magnitude (~5 mm) to handle common interactions with desktop/office items.