[quote=@Dead Cruiser]
[@Hank] I guess I didn't interpret that to mean that they had cut off contact from the outside world, otherwise they wouldn't hear about another dragonborn to serve.

In any case I can reconfigure my character a bit. At his core what I'm planning is a Khajiit monk sort of character, but I'm still working on his motivations.
[/quote]

That is true. What you can do is have your character be an informant for the Blades in that regard, but in a sleeper agent sort of way. Until there is a new Dragonborn revealed, there is nothing to communicate and the connection is purely a passive one.

Perhaps your character thinks that Isobel might be a Dragonborn, and joins the rebellion to observe her from up close and see if she fits the bill? I don't exactly know how the Blades test for the presence of dragon souls without dragons to take souls from, but we can work something out.