On the timeline: once we enter the stabilization phase (which is keeping many of us busy right now), a whitepaper describing the model will be published.
A UX/design document explaining the mechanics of the system should also land during stabilization, together with a description of the parameter space.
It is not yet fully clear whether the dedicated testnet for this feature will be available immediately after the U proposal release, as we want to avoid overlapping with the purpose of Unet during the on-chain governance period.
Regarding the broader point about implementation appearing before design documentation:
While I understand the desire to share designs early for discussion, in practice, we often need to implement the critical pieces of a mechanism before we can present a coherent design externally. Some protocol ideas only become fully understandable once the mechanics exist in code and edge cases have been worked through. Implementing those primitives helps clarify accounting models, allocation behavior, and operational constraints (feasibility and risk).
That said, the presence of code does not mean the design is fixed. Code can still be modified, refactored, or even removed based on feedback during the stabilization and governance phases, before any activation decision. This is part of the cost we accept to make the mechanism concrete and testable early.
The staged rollout is meant to reflect that process. In proposal U, the mechanism is introduced behind a feature flag so that it can be exercised on a dedicated testnet and evaluated by the community. The goal during that phase is precisely to gather feedback, test allocation behavior, and refine parameters (for example by testing alternatives such as the one suggested by @KDprogs).
Activation with finalized parameters would only happen in a later proposal (V), once those aspects have been evaluated through experimentation and discussion.
If there are specific thoughts on the allocation mechanism, parameter bounds, or test scenarios, those can be explored during the experimentation phase, once further documentation is shared.