In his remarkable homily on the "forth" [sic] Sunday of Lent, Cardinal Cantalamessa said: "I have great respect for the venerable Eucharistic Prayer of the Roman Canon, and love to use it occasionally, being the one with which I was ordained a priest.".
"Occasionally". What the General Instruction says is that this Prayer, Prayer I, is: "semper adhiberi potest". It does not say that about any other Eucharistic Prayer. It goes on to recommend it (opportunius dicitur) in Masses where there is a proper Hanc igitur provided; on festivals of Saints and and Apostles which get a mention in this Prayer; and on Sundays.
[It recommends that Prayer II, the ultra-brief pseudo-Hippolytan prayer, be used (opportunius sumitur) on weekdays.]
I don't know what the total number of days when Prayer I, the Roman Canon, would be used if these recommendations of the Instructio were followed ... but I think it comes to something rather more than "occasionally".
In any case, it rather looks as though the Roman Canon is the 'fall-back' canon to be used unless there are pressing reasons for using another one.
So that is what the Novus Ordo itself actually recommends.
"Occasionally", indeed. [The three languages in which this homily was published offer these versions: of the English "occasionally": ancora qualche volta; a veces; encore parfois.]
It is noticeable that friends of the Novus Ordo, such as Cantalamessa, are very shy about playing their own favoured game according to its own recommended rules.