Eager Index Spools Should Generate Wait Stats
In query plans where an Eager Index Spool is directly after a data access operator, wait stats should be generated while the Spool is built. In a parallel plan, EXECSYNC waits are generated, but in a serial plan, you don't see anything. Problem scenarios will become more common when FROID is released and adopted.
I would not expect this to happen when a Lazy Index Spool occurs above a subtree.