There is no barrier to Usmanovs investment, if he wishes to proceed, other than Moshiri's vanity in wishing to go it alone.
I am greatly encouraged by the reports of Usmanovs meeting with Ancelotti, I don't think there is any way he would be manager here without credible guarantees concerning the resources that will be available over the next four years. Those guarantees could not be provided by Moshiri alone given his personal wealth and the state of the club's finances.
I can't really see why Usmanov would be so keen to publicly float the idea of investing if there is nothing in it. Funding a significant proportion of the stadium build in return for equity appears to be the way to go given the limitations with FFP. I could see another holding company being formed to cover that investment, majority owned by Usmanov but with Moshiri as the face of the operation and de-facto boss at Everton albeit symbolically only.
The relationship with Usmanov is already formalised at the club through the sponsorship agreements, in the meantime the reports of a more significant investment have persisted since Moshiri's arrival. The man himself has now been quoted in a very established and serious publication that it would be a "pleasure" for him to invest.
We may have to be patient, but I think if And when PP is granted for the stadium then things with Usmanov might progress in tandem.
We need his resources. If this can happen then it must.