I understand that you don't want to make players feel forced into more complicated hotbar setups to achieve maximum effectiveness. That's fine. And without skill points, your hotbar is the limit on how many attacks you can use. However, the second toolbar is more than just another layer of DPS and buffs...I use my second toolbar for:
-Tracking my Ultimate cooldown. Its obviously not worth a main toolbar slot, but its useful to be able to quickly hit a button and see how long till its done, without having the entire Powers Panel covering the screen (I don't think it shows you the CD anyway, does it?)
-Utility skills and items...at least Travel powers have their own cooldown now, and Toggles will be gone, but Zigg (assuming it still maintains its function) usually goes on my second bar, CC breakers, long-CD steroids, defensive bubbles, permanent and long-term summons. Potentially boosts and other consumables. Things that you don't need to be activating every rotation, but still need to occasionally have available.
If we're only allowed 8 slots altogether, I think that's a disadvantage to summoners (especially summoners like Magik who have several different summon powers), because they're forced into overly simplistic rotations with their summons permanently locking up limited hotbar space.
I also worry if we only have 8 slots, no one's going to want to devote one to a limited-use skill like CC breaks or defensive bubbles, over taking as many damage layers as you can support.
So, I'd propose that the second bar be retained as an option, with the default state set to "off". So new players aren't overwhelmed with too many options, but veteran players who understand the system can expand their functionality.
It'd probably be necessary to make the second bar limited to not allow direct-damage "attack" skills, so you couldn't just layer up every attack in the hero's arsenal...maybe just Summons, Activated Items (which includes boosts), skills that do no direct damage, and your Ultimate.