For the Typicon to function properly it seems that the Menaion and Paschalion have to be on the same calendar. The New Calendar jurisdictions have kept the Old Calendar Paschalion while changing to a New Calendar Menaion. Is there something inherent in the Paschalion that is the reason it has not been changed as well? If the only issues are astronomical accuracy and staying in sync with the civil calendar then we should all switch completely to the Gregorian Calendar. If there are other ecclesiologically more important issues built into the fabric of the dating of Pascha (and its interaction with the Menaion) that will not allow the change then why create a hybrid calendar? Many other cultures and religions get along quite nicely with separate religious and civil calendars, why not us as well?
If I may be indulged...
I see a parallel here with an element of my Anglican past. In late mediaeval, Catholic England, the people seldom received communion. In most places, the norm was for the mass to be offered and for the priest alone to receive, with the people only receiving communion at Easter. The result of this was a curious development in the devotions of the people, to compensate for the fact that they only rarely received communion. Processions of the sacrament were great occasions and featured more highly in the people's experience than the actual reception of the sacrament.
In The Stripping of the Altars
, mediaeval Christian historian Eamonn Duffy writes of the "squints" in the walls of churches. These were small holes/slits cut in the walls and screens of the chapels within a church, in order to enable priests offering simultaneous masses at different altars within the church to see their brother priests. This was to facilitate the most bizarre exercise. Those familiar with the western mass will know that, after the dominical words "This is my body...", the priest elevates the bread for the adoration of the people. Well these holes (some of which survive to this day) were placed there so that priests could see their fellow priests offering the mass, and they would "stagger" the elevations nto ensure that they did not happen at the same time. This was to allow any lay people who may have been present to run from altar to altar to catch a glimpse of the consecrated bread being elevated. The people had been so far removed from regular reception of communion that they had to resort to this.
Protestantism objected to this, (and rightly so), as it was perceived as sacerdotalism. Different churches dealt with it differently. The Anglican church included in its articles of religion the following statement:
"The Sacraments were not ordained of Christ to be gazed upon, or to be carried about, but that we should duly use them."
This was clearly a condemnation of the situation that had become prevalent in earlier times. It was not saying that devotions and processions should not happen, but merely that they were not the reason for the sacrament's existence and so should not cloud that reason. However, today, many Evangelical Anglicans, completely disregarding the original intention beind this statement, use it as an argument against their co-religionists of an Anglo-Catholic tradition, who still have the processions and other devotions surrounding the sacrament. Meanwhile, these Evangelical objectors often have communion only once a fortnight or even once a month, as opposed to their Anglo-Catholic brethren, who often offer the mass with communion every day. The point of all of that is to say that these objectors take the plain words, remove them from the context in which they were written, and read them legalistically to justify their custom of eschewing such devotions. Meanwhile, their own people seldom have the opportunity to receive communion, which is precisely the problem that the statement was condemning in the first place!
It is an example of self-serving, legalistic casuistry at its finest, and I am afraid that I see a parallel in Orthodoxy where the calendar is concerned.
My understanding of the New Calendarists' retention of the Church calendar for the paschalion while using the Meletian calendar for the solar cycle is that it is reflective of the same sort of legalism. When the Gregorian calendar was anathematised, this was accompanied by a strong focus on the condemnation of the departure from the Church paschalion. The menologion did not receive the same degree of specific focus. Those who follow the Meletian calendar are not actually following the Gregorian solar cycle but merely something very close to it, (so similar that the two are identical for the first 800 years). So essentially, for the first eight centuries, they are using the Gregorian solar calendar but are able to call it by a different name, thus escaping the anathema. While it is clear from the expression and context of those anathemas from the late 16th century, that a departure from the use of the Church calendar is frowned upon, a legalistic reading of the wording of the anathemas means that it is possible for the New Calendarist churches to change the solar cycle to the degree that they have without technically transgressing the written norms, provided that they retain the Church paschalion and ensure that there is some difference, however minuscule, between what they use and the condemned Gregorian calendar. It is a case of getting away with as much change as possible while taking care to conform to the minutiae of the letter of the law, while the intention behind those anathemas and the spirit in which they were written is quietly forgotten.My own view
on this sort of approach to Orthodox Church life is probably clear from the wording I have used so I needn't make it explicit here. However, that's my understanding of the answer to your question. I am open to correction.