Been thinking more about this.
Right now DDO has 12 classes, and your class level split is usually the most defining thing about your character. After this change, PrE choice(s) will take over.
In a way, it will feel like we have thirty-something classes.
The 'Barbarian' that joins your group will be less of a 'Pure Barbarian 20' and more of a 'Frenzied Berserker 46/Occult Slayer 30/Ravager 4' multiclass.
And the Rog13/Ftr6/Mnk1 with the quarterstaff will be more of a 'Acrobat 30/Kensai 20/Assassin 15/Half-Orc Ravager 15'.
While this will likely bust up some builds fairly badly I expect - especially Rog2/4/7 splashes (the Haste Boost + Sneak Attack enhancement splashes, like Blitz builds) - I expect it won't be as significant a buildbreaker as some other recent changes. Remember what the Update 9 changes to Epics did to Heavy Pick melee, or what the Update 11 raidboss physical DPS increases did to Warforged melee tanks?