Agreed - so a new "genesis" block would have to be the balance of all accounts from before the last possible "re-org" point.

BTW - said "genesis" block is going to become "huge" in the future (if we had one million accounts then surely we are talking 200-300 MB which you are not very likely to be able to be sending to nodes very quickly - or are we working on some sort of special format to "compress" a genesis block?).

Although it could be divisive it might also be worth "pruning" tiny balance accounts (ones with less than or equal to the minimum fee say) and having those as "fee rewards" for the construction of the new genesis block (this gives some added incentive to create it rather than just to "skip your turn" because of the "work involved").