> 1. There is limited adjustment potential.
What kind of adjustment are you missing? Is is lack of degrees of freedom on the arm or is it the bed?
> 2. The keyboard is not positioned correctly in full supination and my typing error rate goes way up. A fully split design may help this.
I also think a fully split keyboard would be essential here. I don't think it'd be comfortable/ergonomic at all to have the keyboard over your body while typing. I think ideally the arms should be spread to a degree (maybe hands at half a foot distance from the legs) to more evenly distribute the body-weight on the bed.
> 3. It's not a good posture for focusing, although it's great for calm viewing.
Are you referring to how it's easier to doze off? Although, that would also be a problem when viewing.