Some answers about I0coin...
Q: What happened (if anything) to i0coin when it was hard-forked? What happened when it "died" early in its life?
A:I0coin was updated to bitcoin 0.8.x base. It fixed some issues, like the asymmetric diffuculty adjustment, block size limits and BIP16/BIP30 IIRC (see original resurrection thread i0coin.snel.it) It 'died' because the client used too much memory, people (and exchanges) didn't want to run it. It was kept alive by a small group of people until I fixed the memory issue.
Q: Who now controls the development of these coins?
A: No official, however the github source code of the latest version is public. I0coin development is controlled by me. Simple onemanshow, stay close to current bitcoin, do not experiment, do not change stuff. Stability is important
Q: What unique security concerns exist for these two coins?
A: IXcoin had (has?) asymmetric difficulty adjustment, which allows 51% attackers to produce more blocks than they should be able to. Also: hashrate is available to attackers without opportunity cost, because they can mine bitcoin and attack IXcoin I0coin at the same time. Large pools can do this attack trivially on I0coin since the hashrate is far behind
Q: What distinguishes a "mature" alt-coin from new, "immature" brethren?
A: iXcoin has been around for 3 years without issue, furthermore it is among the top 4 in hash rate among all coins. I0coin is almost as old as IXcoin, has a reasonable hashrate.
Q: Will pools drop these coins when rewards are tx fee-only?
A: This is unknown. Mining is free, why would they drop it?
Q: What compelling reason do pools have to merge mine the coins if transaction fees, coin activity, and coin value are low?
A: iXcoin has been merged mined most of its life. We have not seen a drop off in mining. Free extras are always nice. Some pools seem to be afraid that the high blockrate of I0coin damages the efficiency of BTC mining, a good implementation of merged mining can't suffer from the high blockrate
Q: How does scarcity affect value, absent much demand?
A: Demand is certainly an issue with iXcoin. We hope innovation will spur demand. Financial instruments should be dependable and boring (personal opinion rsnel), no innovation in I0coin (except following bitcoin)
Q: Why is IXCoin currently worth more than I0Coin?
A: There are more I0coin, I0coin is traded in only one exchange, iXcoin has a massive hash rate that dwarfs I0Coin. Agree