First, I'm glad you asked for your eggs to be clicked, touching would be another matter

Your idea about the kyubbi being able to get out is interesting, but I don't think that is possible. Otherwise, it should have been able to come out when Naruto was not strong (I mean, before he entered the academy and during the whole of his childhood).
And about the seal, we all know it is a bit lose, yet I think it is very strong. For some reason, kyubbi is unside a cage, and 8-tails is not inside a cage when killer-bee is seen "inside his own self". This shows that:
1 - the 9-tail's seal is still stronger than, at least, the 8-tail's
2 - it is possible to have your bijuu with a lose seal, as killer-bee does not have his bijuu inside a "prison".