ServiceRegistry: Staking

[wjmelements]

I proposed a registry to Airswap a few years ago and I think some of its ideas could be transferrable here.

airswap/airswap-aips#12

One idea there is that there is a fixed cost to adding yourself to the registry, plus an additional cost for additional capabilities. This was to discourage declaring duplicate registrations and false capabilities. Another idea was to refund users when they deregister. It wouldn't have to be a complete refund. The combined effect is that the registry provides better information and is less likely to accumulate garbage.

Originally posted by @wjmelements in #142 (comment)

[wjmelements]

Abstract

A staking incentive would help curate the registry.

Motivation

If it is too cheap to add to the registry then the registry may become full of ads, hate, or other noise.
If there is a refund for leaving the registry then there is an incentive to remove one's self from the registry when you stop being a service.
The overall benefit is that the data in the registry is less noisy and cluttered, and therefore its information is better-curated.

Specification

• registration requires a large FIL deposit
• signaling capability requires a smaller FIL deposit
• delisting capabilities refunds most or all of the per-capability deposit
• deregistration refunds most or all of the registration deposit

Complete vs Partial Refund

A complete refund is kindest to those registering and fairest in the event of migration.
The benefit of a partial refund is that it will be costly to repeatedly register and deregister.
The remainder would be burned.

If the registry is upgradeable then the burning could be delayed until withdrawal.
This way, in the event of registry migration, the burning could be removed so that stake could be transferred to the new contract.

[rvagg]

A complete refund is kindest to those registering and fairest in the event of migration.

Could we implement a migraiton method in here that pushes an entry to a new contract and that (optionally) bypasses the need to pay for an entry in the new contract? So we always burn, never hold funds for refund, but a new contract just has a migration method that allows migration from an old contract at a specific address and that method can opt to not take a fee (or maybe some minor fee diff if there's a cost change between the upgrades) since the SP already paid a fee to be in the old contract.