Despite the code changes from 2.29.6 suggesting otherwise, casting an empowered spell as an Evoker still does not show the number of stages of said spell cast. Blizzard should provide enough information about the cast to, if it were impossible to obtain the breakpoints of each stage, calculate them based on the retrieved cast time (which appears to be 30/20/20/30 percent of the total cast time).

/knp dump

2.29.6 2.5
enUS EVOKER
{profile=default}
{castbar_detach=true,castbar_detach_height=14,castbar_detach_nameonly=true,castbar_detach_width=200,castbar_icon=false,castbar_name_vertical_offset=0,castbar_shield=false,castbar_showpersonal=true,classpowers_on_target=false,classpowers_size=20,classpowers_y=30,cvar_enable=true,cvar_name_only=true,cvar_personal_show_always=true,cvar_personal_show_target=true,frame_height=24,frame_height_personal=30,frame_minus_size=false,frame_target_size=false,frame_width=200,frame_width_personal=200,powerbar_height=10,threat_brackets=true}
HealthBar, CombatUpdate, NameText, LevelText, RaidIcon, ClassPowers, CastBar, Highlight, PowerBar, AbsorbBar, Threat, Auras, Classification, Execute, TankMode, Fading, GuildText, PlayerAnchor, [CombatToggle], ArenaID, BossMods, Quest, BarAnimation, Target

Yeah it only shows the basic cast bar for now, no stages yet