NECESSITY OF A NEW BLOCKCHAIN
The whitepaper states that colored coins inherit the same limitations as the bitcoin protocol. Metacoins do not, but they cannot be truly secure without having a copy of the blockchain. How big of a problem is this? Hasn't the Electrum model worked for Bitcoin? Is there a big issue with just querying a bunch of supernodes to see if they all give the same result? Is it necessary to have absolute security with every contract, or only very high value transactions? Is it correct that metacoin clients won't need the first 14gb of the blockchain?
BITCOIN BLOCKCHAIN SIZE
Bitcoin Magazine's analysis showed that since storage capacity and internet bandwidth follow Moore's law, the blockchain size will not be a problem to store on phones. How many years from now should we predict that the blockchain size will become irrelevant? If the blockchain size were irrelevant, would ethereum still be necessary? How much demand is there for blockchain contracts at this time, and how fast should we expect demand to accelerate?
ETHEREUM BLOCKCHAIN
How fast should we estimate the ethereum blockchain size will grow? What will be the effects of ethereum blockchain size growth several orders of magnitude greater than Bitcoin? Will this lead to more mining centralisation?
TURING COMPLETENESS
Is it reasonable to think the client can be sandboxed? What will be the effects of these, since the protocol is Turing complete: viruses, malware, adware, keyloggers, scam contracts, wallet stealers
ILLEGAL CONTRACTS
What will be the effects of illegal contracts? An assassination market, for example? Will the Silk Road be able to run on ethereum? Will a database of child porn be able to be stored? If there is child porn stored on the blockchain that is easily accessible, will it be legal to store the blockchain in any country? What will be the effects of running all the clients over Tor by default? Can a 60s block time with huge blocks work over Tor?
SATOSHI'S ARGUMENTS
In 2010, satoshi succesfully argued against including Namecoin into bitcoin, suggesting merge-mining instead.
"Piling every proof-of-work quorum system in the world into one dataset doesn't scale.
Bitcoin and BitDNS can be used separately. Users shouldn't have to download all of both to use one or the other. BitDNS users may not want to download everything the next several unrelated networks decide to pile in either.
The networks need to have separate fates. BitDNS users might be completely liberal about adding any large data features since relatively few domain registrars are needed, while Bitcoin users might get increasingly tyrannical about limiting the size of the chain so it's easy for lots of users and small devices." -- Satoshi