For anyone who's reading this later: You can still Z-order your materialized views, but you can't run it as a SQL command. Instead, you can set it as one of the TBLPROPERTIES when you define the table. Here's an example:

create or refresh live table {new_table}
tblproperties (
	"quality" = "gold",
	"pipelines.autoOptimize.zOrderCols" = "KEY_1,KEY_2"
)
as
select * from {old_table}

This won't Z-order things immediately, but it will do the Z-ordering during the pipeline's maintenance job. It also means that your tables won't be Z-ordered until the maintenance job has run, and to my knowledge you have little control over when it will run. This can be a problem if you're running the pipelines on a daily basis.