I have been involved with cad layering systems on both sides of the fence - or is it all four sides? Client, consultant, AutoCAD and MicroStation. Anyway, I've had to use numbers only and named layers. NCS, while not perfect, is also as good as any I have seen, and in some cases, way better than others.
We have a number of clients that use an NCS like system, with either no discipline letter, a single letter or two letters. We had a mixed standard in LD where if the largest client (no discipline letter) had a layer, we used it, but when there was nothing in the clients layers to match what we needed, we used NCS like layers. When our second largest client adopted an X-XXXX-XXXX... NCS and we had to migrate to Civil 3D, it made sense to cut from the past and adopt NCS 100%.
I was also on a team of consultants that assisted our local DOT on their migration to MicroStation V8. (10+/- years ago, by now.) Actually, I was at the DOT as both an employee and as one of the larger departments' CAD Managers when they developed their pre-V8 standards (all numbers, 1-63, lots of external references since you only had 63 layers) and since leaving has seen what other DOT's had done with named levels.
I really had to stress that just because you now had named levels, that some restraint was called for. I'd seen some where the layer names were so verbose that you needed an extra wide layer dropdown menu, and others that base their layers on the codes the survey crews used - so short that you needed a lookup table to know what layer to use and many that seemed to by striving to get in Guinness for having the most layer names in existence.
But while we kept the raw number of layers down, we lost the battle over keeping a discipline letter as part of the layer name. They believed you did not need it since the filename also implied a discipline. But then, we also lost the battle on using bylayer. But that's a whole other story.