Conversation uses ancestry string

[ernsheong]

From https://github.com/stefankroes/ancestry, the README says:

In the example above, the ancestry column is created as a string. This puts a limitation on the depth of the tree of about 40 or 50 levels, which I think may be enough for most users.

Doesn't this put a severe limitation on conversations using this gem? It's not safe to always reply to the latest message when using this gem, as the ancestry string may overflow. But it should be okay to reply to the first message in the conversation.