this is cute and imaginative, but it is better as fiction than as social science or prediction. if the professional economists can't predict anything two years ahead, why do you think you can?

1. even if bitcoin were untaxable, which it's not, why would the government be unable to find some other source of funds? it could tax land (owners or renters), for example. at the very worst, tax fraud through bitcoin could slightly undermine progressive income taxation, but it's unlikely to do even that because there would still be real-world employers with physical presences that are easy targets of tax enforcement. most salary-based tax is voluntarily reported by individuals, except for that portion declared by institutional employers. your view is a bit ahistorical, too: the income tax isn't even very old.

2. you seem to be assuming that the value of an individual bitcoin will reach $1 million. (that is probably what would be necessary for satoshi to be a 'trillionaire'.) why would anyone without bitcoins throw so much money into bitcoins, however? they might be useful, and they might be enough to attract both speculation and real use, but a century before your fanciful claims would materialise, those with present wealth would find it far easier to set up an alternative cryptocurrency.

2a. bitcoin would not actually be a robust way to store the amount of wealth that would be necessary for your story to materialise. it could still probably be disrupted by $5 million's worth of asic chips. it presently stores, also, nowhere near as much as the widely reported 'market capitalisation' figure.

3. why do you think bitcoin enables your nightmare scenarios, like kidnapping children in the suburban united states to sell them to paedophiles? if there were already drive to do this and people thought they could get away with it, i'm sure suitcases of cash or wire transfers to borderline-lawless jurisdictions would make for suitable, less trackable payments.