The Septuagint is in a form of Greek known as "Septuagint Greek," between Attic and Koine.
The New Testament was written in Koine, except for the first two chapters of Luke after the first verse of two, which appear to most scholars to purposefully mimic Septuagint Greek.
Except for Hebrews (and the works of Luke) the Koine Greek of the New Testament can be difficult to read. The Pauline epistles are sloppy and Johannine works are repetitive, though one can find a beauty out of the Johannine works. Hebrews is excellent, and Luke writes very well, albeit like a skilled fictional writer more than an historian (for instance his claim that Jesus ascended on Easter Sunday at the end of his gospel but then his beautiful reinterpretation of it as a forty-day later event that takes place from the Mount of Olives in a Moses-like event as a prologue to Acts as one of many irreconcilable examples). Matthew may have once been a translation from Aramaic, but there is little evidence of this in its present form.
The Greek of both the Septuagint and the New Testament do not match, neither are they modern Greek. There is no need for a modern Greek NWT for the general Greek public that grows up going to Greek school learn ancient forms of Greek in order to follow along with Greek liturgy (written in Koine) in churches. The Watchtower wastes their time making things like this because they are ignorant of Liturgy and the importance of it in religions.