2: Then if BIP110-coin eventually lasts long enough to reach the difficulty adjustment period without any increase of hashrate, it would be a significant (99%) drop in difficulty requirement making BIP110-coin vulnerable to 51% attacks, orphaned blocks, double spends, and transaction censorship.
Doesn't change much, but there's a 4x limit on difficulty adjustments, so the difficulty would drop by 75%, not 99%:
// Verify that the difficulty isn't growing too fast; an adversary with
// limited hashing capability has a greater chance of producing a high
// work chain if they compress the work into as few blocks as possible,
// so don't let anyone give a chain that would violate the difficulty
// adjustment maximum.
if (!PermittedDifficultyTransition(m_consensus_params, next_height,
m_last_header_received.nBits, current.nBits)) {
LogDebug(BCLog::NET, "Initial headers sync aborted with peer=%d: invalid difficulty transition at height=%i (presync phase)\n", m_id, next_height);
return false;
}
Doesn't change much, but there's a 4x limit on difficulty adjustments, so the difficulty would drop by 75%, not 99%:
// Verify that the difficulty isn't growing too fast; an adversary with // limited hashing capability has a greater chance of producing a high // work chain if they compress the work into as few blocks as possible, // so don't let anyone give a chain that would violate the difficulty // adjustment maximum. if (!PermittedDifficultyTransition(m_consensus_params, next_height, m_last_header_received.nBits, current.nBits)) { LogDebug(BCLog::NET, "Initial headers sync aborted with peer=%d: invalid difficulty transition at height=%i (presync phase)\n", m_id, next_height); return false; }source
See also this Bitcoin StackExchange question.