I think the highlight of this proposal is the dynamic SAFE parameters - tx fees and time-weighted value stored. This is an excellent approach.
However, the rest of the proposal fights against the strength of these parameters.
Rewarding mainnet safes exclusively seems brutal. I mostly agree with the third point @calchulus made: safes created before any reasonable expectation for airdrop would filter most sybil attackers (even then, I don’t think this filtering is necessary here - see further below).
The “meaningful amount” goal seems to rise from that mainnet-centric strategy, which is a self-inflicted problem. While Safe spun out from Gnosis, it still grew as Gnosis Safe. Why not use (and encourage use) of the ecosystem the same way Cowswap did? Remove the 400 minimum. Let the bigger safes claim on Ethereum, and have all the smaller safes (be it Ethereum, rollups or altchains) claim on Gnosischain.
Going further, once we forget any minimum amount, and determine airdrop amount solely on gas spent and time-weighted value stored, there’s hardly a downside to rewarding every Safe - before or after feb9 2022. A would-be Sybil attacker who made 100 Safes on a cheap altchain and did 2 transactions on each for a total of ~$20 spent in gas fees would get the same amount as a legitimate historical user who opened a Safe on Ethereum and did one transaction costing him ~$20 in gas. All things considered, legitimate users with a rich Safe history and ample funds should dwarf any Sybil attempt.
If nothing else, skipping Gnosischain users is a strong negative signal against taking chances on the Gnosis ecosystem. Indexing airdrop amount on the Safe ETH/dollar values and/or gas spent would likely result in a minimal decrease for the bigger participants anyway, as I’d wager the amounts involved are negligible. Gnosis Safes secure billions of TVL on mainnet, while the entire TVL of Gnosischain is ~$220M.
As stated, I think the plan would fall short of its first bullet point - “decentralize through wide distribution”.
And needlessly so!
The dynamic SAFE allocation parameters (tx fees and time-weighted value stored) are excellent equalizers. An airdrop solely based on these settings would be unopinionated, decentralized, reward usage, raise awareness and let every current Safe holder feel ownership.