[Supermighty]

> since if they start with a brand new root certificate then I'm not sure what happens with the older browsers.

IdenTrust will cross-sign Let's Encrypt root cert. I imagine they will keep it cross-signed, for backwards compatibility, once LE has their root cert in all the browsers.

[iancarroll]

You can't exactly undo cross signing without creating a new root CA - at some point they'll probably stop sending their root CA with the handshake (which is required when cross signing).