I applaud the OP's proposed formula, and do not wish to be negative at all. On the contrary.
But, it seems to me that there have been many such formulas which received a necessary degree of acceptance but which still failed to bring about a reunion. It is certainly not necessary to prove fault on one side, and although this is deusveritasest's view, it is not one which has even found acceptance in Orthodox history.
When the Georgian non-Chalcedonian Church came into communion with the Byzantines (mostly for political reasons) there was no finding of fault. A union simply took place and Chalcedon was accepted. Likewise when the union briefly took place in Alexandria in the 7th century there was no finding of fault, rather a recognition that the same substantial faith was held. At the various 6th century conferences which took place there was a general acceptance that the same faith was held. And in 1851 when the Greek Patriarch of Alexandria planned to enter into union with the Coptic Orthodox Patriarchate and become a Metropolitan there was no issue with the substance of the faith.
The Henotikon, as one example, was broadly acceptable to all on the level of the Christology it described. St Severus accepted it as far as it went.
But... many of these opportunities have foundered over the issue of Chalcedon. I do not say this either positively or negatively, but as stating a matter of fact. Many of the early conferences achieved agreement on Christology quite easily - because there is substantial agreement on Christology. This is why the non-Chalcedonians have always accepted Chalcedonians into communion by confession of faith and not by (re)baptism, and have received clergy in their orders, usually requiring a period of probation to prove their stability.
But Chalcedon has been, and remains, a stumbling block. Certainly not an irreducible one as far as I can see. But it is one that cannot be ignored, and therefore in any reunion it must be faced and dealt with, as, to a lesser extent, must the other councils.
If I might be a little critical of your statement, I would say that you fail to properly represent what is meant by one will and one nature and one energy within our non-Chalcedonian, and, we would insist, Cyrilline Christology. It would seem to me that it would be advantageous for any such text to show that it understood the value and importance of these terms and was not simply excusing them. I certainly confess one will in Christ, but I am pretty sure that what I confess is not what you might understand, and is not what is condemned as monothelitism.
I would also not find it acceptable for Theodore of Mopsuestia to be considered a Father at all in any reunited communion. This is because what he DID teach is error, and St Cyril considered it utter error. He preserved him from a posthumous anathema for the sake of the unity of the Church not because he accepted his Christology at all.
Constantinople 553 is very clear...
If anyone defends the impious Theodore of Mopsuestia ... and if anyone does not anathematize him ... let him be anathema.
Leo is a different case. There is room for excusing his Christological language, considering what he meant, etc etc. And surely in any case, certainly as far as I am concerned, he was ecclesiologically heterodox, and even heterodox in his Trinitarian thought, much more than his Christology.
My personal opinion is that there should be much more inter-communication of theological explanations and questions. (I am grateful that an article of mine has been published in a Serbian theological journal for instance). But at some point it seems to me, the text of a council such as Constantinople 553 should be presented to the Holy Synods of the Oriental Orthodox, glossed with necessary explanatory material, and offered for reception as an Orthodox (not necessarily ecumenical) statement. If the Oriental Orthodox synods could accept Constantinople 553 as an Orthodox statement, with explanatory glosses, then this might be a necessary step forward.
It would require, on the Eastern Orthodox side, that they allowed that the text could be received apart from the event. I think that Constantinople 553 would be the easiest to deal with. It would provide some sort of a model for the other conciliar statements. At some point the Eastern Orthodox would need to consider what was important and what was necessary. To say that a statement is Orthodox is not the same as to say that it is ecumenical, and it is certainly not the same as saying that the historical narrative that has been built up by the Eastern Orthodox around these issues is acceptable.
I could, for instance, imagine accepting the text of Chalcedon even, as Orthodox, with suitable glosses to show what is meant when the Eastern Orthodox use it. But I could never accept the narrative built up around the event of Chalcedon in 451 which I consider biased and false. (I am not wanting to argue about that at all). But if the text can be separated from the event then there is the possibility of agreement, if the event must be understood as most Eastern Orthodox presently choose to describe it, then there is no possibility of reunion ever - which is the same outcome as has always been the case.
What matters? The Eastern Orthodox must reflect on this. Is it that there is agreement on the substance of the faith, or that there is agreement on the historical narrative which has built up around each event? If it is the first, then agreement has already been shown to be possible time and again through Church history. If it is the latter, then we will find that progress fails at the same point.
