Crapes tend to have a not very promising outlook in the Puget Sound area. While the plants will generally survive okay, flowering is typically very limited in all but the most heat reflective situations - it simply seldom gets hot enough here for long enough to stimulate blooming on a reliable basis. Some of the older hybrid cultivars - like 'Natchez' or 'Cherokee' - will produce flowers in most summers if well sited but have yet to see any of the more recent introductions have similar results. In general, these shrubs just tend not to be great selections for the PNW.

For a somewhat similar effect, I'd look at one of the dark leaved ninebarks or Sambucus (elderberry). At least you will be assured of flowers with them.

Or maybe a purple Cotinus. With one of those the flower heads would also be conical. Otherwise, if you can do without the purple leaves Heptacodium miconioides is superficially similar to a white crepe myrtle in bloom. Or if you want bigger "petals" there is always Hydrangea paniculata or H. quercifolia.

The leaves of the last one turn purple in fall at least.