Frankly, I am not as fervent an admirer of Ven Pius XII as many of my readers will be. Three of my reasons:
(1) He initiated the concept of deeply radical 'revision' and transformation of the Liturgy, which ended up we-know-where; and
(2) he developed significantly the disastrous and sick modern papal personality cult: I detect a direct line from him through S Paul VI to PF. Joseph Ratzinger wrote "After Vatican II the impression arose that the pope really could do anything ... "; it was a small jump from this to the major Bergoglianist error that PF, free from the constraints of Scripture and Tradition, is guided in his daily words and deeds by the Holy Ghost, by whose intervention he was indeed elected.
I do not subscribe to this perversion of Catholicism. So the idea that Pius XII's canonisation might be brought nearer by the opening of the remaining Vatican Archives of his pontificate leaves me, er, tepid.
(3) It is the role of the Roman Pontiff to repel error and to condemn heretical innovation. Nazism was a gross conceptual error; more precisely, it was a form of the Marcionite Heresy which the See of S Peter had put down in the Second Century. ("To Rome comes Marcion, already under censure in other Churches; but until Rome has condemned him he is still a Catholic Christian": Dix.) Between 1939 and 1945, this heresy was made even worse by the inclusion of anti-Christian twaddle such as Earth, Blood, and Volk. And it did not meekly remain in the lecture room: it was horribly embodied in an unjust war of aggression and in the planned mechanised slaughter of millions.
Yet, during this period, there was no papal condemnation of the error, or specifically of the consequent Judaeicide, at the formal, Magisterial, level. The fact that Pius XI had condemned it should have made it easier for Pius XII to repeat and to develop and to precision and to elevate (why not ex cathedra?) that condemnation both at the conceptual and at the genocidal levels. In the Newman terminology which I endlessly promote, the Teaching Office of the Church was, at least arguably, as much "in suspense" from 1939 to 1945 as it was during the Arian Crisis and has been during this pontificate. It is not that Pius XII taught nothing during those years (Mystici Corporis ...), so much as that he failed to teach with proportionate vigour and focus about the biggest single monstrous error that was staring Europe in the face. Just so, Vatican II was to leave Stalinism not, indeed, exactly uncondemned, but possibly not adequately condemned. The early Church Councils, on the other hand, identified errors by name, and flung precisely worded anathemata around with accurate addresses on the envelopes.
So there you have my own, provisional, personal,view.
I am a person of very imperfect judgement. I am usually wrong. My wife will confirm this.
So, if the opening of the Archives gives us a quite different picture of that pontificate, then, if I am still alive, I shall welcome it and do penance.
[I wonder if the Yad Vashem people and those neo-con meejah folks across the water would also welcome such a result. Or would they dream up some new means of evading the consequences of newly disclosed facts?]
(I know Pius XII secured the survival of nearly a milllion Jews who would otherwise probably not have survived, so please don't inform me of this. Let's take it as agreed between us.)