Thanks for your questions!
Let me try to answer them:
1 - The subnets will store the UTXOs (roughly 4-10 GB in size depending on data representation) and not hold on to the blocks themselves. So, the Bitcoin integration is not expected to have a significant impact on subnet capacity.
2 - I’m not sure what you mean by “second part” but there are several differences between a lightning channel and a Bitcoin smart contract on the IC. In short, the Lightning network offers bidirectional payment channels for off-ledger transactions. Bitcoin smart contracts on the IC offer arbitrary smart contract logic for Bitcoin that (potentially) any user can interact with.
Smart contracts on the IC further do not have the shortcomings often associated with the Lightning network such as the risk of a fraudulent force close or the risk of establishing “hubs” that constitute endpoints of large number of channels (whose failure may have a detrimental effect on the whole network).
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