A Japan outside the Pacific War redirects Allied and Soviet strategy

Would Japan postponing war with the West until 1948 strengthen Stalin's demand for battleships?

Yes; Japan would remain a visible Pacific threat while an earlier European victory could free the Soviet Union to resume blue-water fleet construction.

Without a Pacific war, Britain does not divert Prince of Wales, Repulse, and an Eastern Fleet, while American resources can concentrate more fully against Germany. The European war could therefore end earlier, leaving the Soviet Union able to revive prewar blue-water plans. A still-expanding Japanese navy and Japanese influence in China would give Stalin an additional reason to demand battleships and other major Pacific units. Neither side would necessarily possess an atomic bomb when their new fleets matured, potentially setting up a later Russo-Japanese conflict.