Easy fix: use different inputs
True, but now I'm splitting up a single output in to 12 UTXOs (for example) up to 12 months in advance, and then signing multiple different timelocked transactions to broadcast later for each one with variable amounts (since the price will definitely change) and variable fees, keeping them all secure, and then choosing which one to broadcast at a later date? And this was supposed to be less work than just making a transaction once a month?
Now that I think about it: you can just as well send small funded private keys on a monthly schedule to pay for your subscription.
Too easily abused. Merchant can sweep it and then respond "That private key was empty, it must have been compromised on your computer/email provider/whatever."
