>I think a lot about Motie engineering versus human engineering. Could Motie engineering be practical? Is human engineering a fundamentally good idea, or is it just a reflection of our working memory of 7 +/- 2? Biology is Motie-esque, but it's pretty obvious we are nowhere near a technology level that could ever bring a biological system up from scratch.

It's the kind of thing you commonly get if you let an unconstrained optimization process run for long enough. It will generally be better, according to whatever function you're optimizing for. The main disadvantage, apart from being hard to understand or modify the design, is manufacturing and repair (needing to make many different parts), but if you have sufficiently good manufacturing technology (e.g. atomic level printers), then that may be a non-issue. And in software it's already feasible: you can see very small scale versions of this in extremely resource-constrained environments where it's worthwhile really trying to optimize things (see some demoscene entries), but it's pretty rare (some tricks that optimizing compilers pull off are similar, but they are generally very local).