From Tad, via the Message Board:

At present, the full last piece (two volumes, now) is at about 1300 pages ms., with another two hundred perhaps to come. That means about 750 pages each in first draft for the new, split books. The first two books published were each about 800 or so in manuscript, so we’re talking about two more very similar sized volumes to SHADOWMARCH and SHADOWPLAY.

Shadowrise will be the third volume in the series. The working title for volume four is Shadowheart.