There may be a way to be in a state of eternal euphoria while still somehow being motivated accomplish things. This could be accomplished by making it so that the brain experiences different levels of euphoria for different things done. there could be for example a standard level of euphoria (laying in bed) and a high lvl of euphoria (winning the lottery, having sex).
This I think would solve the problem of destructive bliss.
Gradients of bliss would definately be a step up from the pain/pleasure axis with the same functional equivalent. I get a stab of pleasure whenever someone proposes this - partly because I'm tired of the 'no progress without pain is the universal unbreakable law' response.
The question of why we subjectively experience suffering... the age old philosophical problem. What purpose for survival would the subjective experience of pain have - I mean why didn't nature create us so that we only experience gradients of bliss?
Why awareness of loss or pain? There are many complex systems that respond and adapt to environment without experiencing suffering - like the immune system.
The immune system simply adapts - there's no need for pain or even pleasure.
Consciousness is a downstream event from decision making and a distorted perception of the biological signals - so what purpose does it serve? Wouldn't unconsciousness be more efficient? Is consciousness merely the creation of a learning experience to be encoded?
Is there a reason why an organism would benefit from being conscious of it's learning process?
Just thoughts...
We've got alot to learn about our design before we'll be able to eliminate suffering through re-design.
In the meantime, the value of eliminating suffering through science can be implemented in a myriad of ways - and help one to lead a more meaningful and satisfying life.