We've already agreed that we prefer Counterparty to use IXC instead of a metacoin, but without being able to excrow IXC then trading will be slower (taking mulitple confirmations) and betting won't be possible. Plus, it would be very easy for one of the Counterparty assets to become the preferred metacoin over IXC, especially if a Counterparty asset can perform the functions faster.
I still don't understand what's the problem with a metacoin (or an asset becoming the prefered metacoin). Those coins are not new altcoins in the sense that they are independent from IXC. Instead, they are are fully dependent on IXC, but IXC is independent on any Counterparty defined asset/coin. There is no way they can "dilute IXC", only (possibly) add value to IXC (through the increased use of IXC, i.e. transaction fees). Those coins are directly traded with IXC in the network, and since you can not even use those coins/assets without owning some IXC (for fees), it makes little sense even to set up a third party exchange (say for metacoin <-> bitcoin). In other words, those interested in Counterparty features will first need to get some IXC.
They are later unlocked and either left with the original owner or sent to a new owner depending on triggers from Counterparty.
And that's the problem. In oder the network to decide where the coins should go,
the network has to understand the Counterparty protocol. That is, the implementation has to be native. Or can you explain a method for an escrow without the network understanding/parsing the protocol?