Regarding graduated wallets, the multiple wallets reference design in the Bitcoin Design Guide goes in that direction. Multiple different setups in the same application for different use cases and appropriate levels of security.
Where the activity seems currently in the ecosystem seems to be around whether Ecash, Ark, Spark, etc have a place at the very low-end for really small amounts.

Bitcoin Design
Multiple wallets
A UX reference design for a multi-key bitcoin wallet designed for both daily spending and storing medium amounts.


What does simple mean to you?