Yes, the Bukito also uses ribbon cables. Almost everything on a typical 3D printer is within spec for a single line on a standard 28awg ribbon cable except the heaters (larger stepper motors are marginal). For those, parallel lines work.
Yes, it is possible for one 28awg wire to have a very slightly lower resistance than another, but it’s not a big effect, and remember that copper has a positive temperature coefficient of resistance, so if one wire is heating more because it is carrying more current, its resistance will increase, bringing it into a closer balance of resistance with the others. This makes the current carried by the multiple lines somewhat self-leveling, rather than a situation where you could get thermal runaway in one wire until it fails, causing a cascading failure in the parallel lines.
Nophead backed his ribbon cables with a thin plastic sheet to enforce a minimum bend radius (similar to a cable chain). I always liked this idea, and we experimented with it for the Bukito, but ultimately decided that it wasn’t a fit for our application. Nophead does NOT use IDC connectors on his, and instead individually solders the wires into D-sub connectors, which I always thought was a dumb idea.
Check the ratings of your wires and connectors (note that the current-carrying ability of ribbon cables is slightly different when you have multiple current-carrying lines adjacent on the cable, since they will both be heating the same bit of insulation). We determined that ours could safely handle 1A per line, and our heaters drew 3.33A @12V, so at least 4 lines were needed. I increased this to 5 for some additional safety margin, and further ganged the high side with a sixth one paired with the switched fan power lines (which did not need a full 1A). Even if a single wire did fail, it would still be well within spec, and a double failure in the same gang would probably still have been ok.
There are ribbon cables you can buy with higher current ratings. Though they are more rare, there are 26AWG cables with the same .05" spacing, compatible with standard IDC connectors. Those will carry more current per line, but at Deezmaker, we decided to go with the more common cables, both for cost reasons and because we wanted to design with the safety margins for it anyway, since we wanted to make it possible for users to create their own cables (we had ideas about selling the boards separately as upgrades and creating standards that never really came to fruition), and knew that if we did, someone would eventually try to use it with the cheapest, lowest-spec’d parts available, and we wanted that to be safe.
The best cables, of course, are silicone-insulated high-flex cables. Not only are they the best for repetitive motion applications, but the insulation can handle much higher temperatures as well. Cicoil sells IDC-terminated high-flex ribbon cables that are supposedly rated for a whopping 5A per line, though my research showed that none of the connector hardware could possibly be rated that high. Still, other than maybe a custom flat-flex cable, I’d say those are probably the best type of cables you could possibly use for moving components in a 3D printer.