Noted, thanks for your feedback.
Having an API to query any bitcoin transaction (spent and unspent) was ruled out initially because of the storage requirements. We’d need to store 100s of GiBs of additional state.
One idea would be to support this API for only “recent” transactions (e.g. transactions from the 24 hours). Another idea would be for the canister to use the HTTP API to fetch this information from some external API.
We can iterate on this and figure out the best step forward as we collect more feedback.