It seems pretty clear that checkpointing by the devs introduces an avenue for corruption/compromise of the chain. But checkpoints are certainly a reasonable approach to preventing forms of DoS and potentially even accelerating new nodes catching up with the chain.

What if we worked towards a check-pointing process based on proof-of-work? It could work something like this:

- A checkpoint is proposed on bitcointalk or reddit or wherever.
- Check-pointing becomes an on-chain transaction, where the block-to-be-checkpointed's hash is included in a tx. It could be earmarked by doing something silly like spending a millibit from the coinbase reward.
- A checkpoint is accepted as valid if it is included in some X of Y blocks in a row in this manner. X could be something like 70 and Y 80, say (to be totally arbitrary). Then the checkpointing processes requires consensus from the whole network, but is not spoiled if a few miners/pools decide they want to be adversarial. If large pools are staunchly anti-checkpoints, then arguably that's the network's decision to make.

Once a checkpoint is conceded on the blockchain, the devs can add it to the source code, and the client can verify that it is indeed a valid checkpoint by finding the first block it is checkpointed in and verifiying the same hash exists in X of Y consecutive blocks. I believe this can be done without a fork (presuming coinbase rewards can be used as inputs within the same block, else we need another way to earmark the special checkpoint txa, but I imagine this shouldn't be too difficult).

Thoughts?