Couple points here. One, there is a separate factory in the Cort complex that makes the Premium basses. It has different woods, different builders, more refined processes than the basic plant. You can tour the factory via video on Youtube, search "Cort Indonesia Factory Tour."
I've seen the Phillip McKnight video on his visit to the Cort factory and was aware that there are separate areas for different 'grades' of instruments.
I'm not familiar with what area produces the mdm1605. Maybe that's what the Premium marking on the headstock means?
Two, Ibanez uses a nylon-based super hard plastic for their nuts. It is very durable and transmits vibration to the neck pretty much the same as bone, but might be more durable than bone. It does not need to be upgraded and it is not a "cost savings" item. The nuts are pre-cut, unlike many bone nuts that are cut at point of assembly. This keeps string spacing at the nut consistent between basses. Both my SRs, the Premium and the fretless, have these and they do the job very well.
Here's the results of a perfunctory search on Google:
Ibanez uses several materials for their bass guitar nuts, primarily determined by the instrument's series and price point. Most standard and entry-level models use plastic or PPS (Polyphenylene sulfide), while premium models often feature branded synthetic materials like GraphTech TUSQ XL.
Common Nut Materials by Series
Standard Series (SR, BTB, Talman, GIO): Most mass-produced Ibanez basses, including many models in the SR and BTB lines, come stock with plastic nuts. Some technical specifications specifically label these as PPS (a high-performance thermoplastic) in colors like ivory or black.
Premium Series: Higher-end models, such as certain SR Premium 6-string basses, use GraphTech TUSQ XL. This material is designed to be self-lubricating to improve tuning stability and sustain.
Common Upgrades
Many players choose to replace stock Ibanez plastic nuts with aftermarket materials to improve tone or tuning stability. Popular options include:
Brass: Known for increased sustain and a brighter, "bell-like" tone.
Bone: Often preferred for a richer, more mellow tone compared to plastic.
GraphTech TUSQ XL: A common synthetic upgrade that reduces string "ping" and improves stability.
Finally, I'm not trying to badmouth or besmirch the good name of Ibanez; rather merely attempting to add info and encourage discussion.
Honestly, I am quite interested in this bass and may well end up purchasing one when they become more readily available.