Well, the great thing about the low-fare airlines is that they seem to be able to create a market for these flights, where previously no such market existed (but the potential was there to be exploited).
I don't see why GO shouldn't offer more and more flights to places such as Prague, and from regional airports.
The only problem is that GO should really try to lower their fares a bit more, as they can be very expensive. They have lots of great offers, but a random booking is still likely to be more expensive than with airlines such as Buzz and Ryanair.
Nevertheless, I do think they could expand to serve Euro destinations from places such as EDI, GLA etc.
They just need to get their marketing up & running (which they are very good at-ever heard the GO theme tune?-very interesting!)