I don't buy this. Everything we've heard so far is that with the infrastructure needed for the retractable pitch, plus the need for all four stands to be in place before the roof can go in, a partial opening is not possible.
I can't see it being feasible at all.
Plus I imagine the club would want to get maximum impact from the whole stadium opening, rather than piecemeal over two seasons, and would want everything to be spot on before it opens. I don't see that the high spec fit-out could be sufficiently completed in the coming close season if building works are still ongoing.
Having said that, I know bugger all about this type of project but it doesn't feel plausible.