is it possible to connect two external monitors with mini displayport + thunderbolt to displayport or hdmi?
The thunderbolt port and display port are the same port.  So it's not two separate ports.

That said, due to the high bandwidth nature of thunderbolt, I suspect we will be able to daisy chain monitors in the future, as well as having thunderbolt "hubs" where multiple devices can be plugged in.

But for now, it's one port.  So only one external monitor.