If the normal process is followed, it will be around October sometime the next expansion is first revealed, the final main content patch (in this case, 7.55) will go live around March next year, and sometime mid next year the expansion will actually launch; probably June or July (EW was an exception due to the chaos and delays caused by COVID). This is how things have usually been handled, and because DT stuck to that too, I see no reason 8.0 will not be the same.