As a Brit my thoughts on the potential for inbound European tourism are mixed.
It is true that the sunbathing British tourist has seen a reduction in options over the last couple of years since Turkey and North Africa became seen by many as being too unsafe. That said, in summer season the market is saturated with cheap LCC options from all major UK airports to destinations accross Portugal, Spain, France, Italy, Greece and Cyprus etc.
Northern hemisphere winter is obviously the logical time for Brits to visit Australia, when the UK is dark and cold from November to March and you're basking in the southern sun. Nowadays, short-medium haul options for sunny weather in these months is more or less limited to the Canary Islands unless you are prepared to fly long haul.
For the tourist that is prepared to fly further, Britain is only 8-9 hours from the Florida and the Caribbean. How is a (more expensive?) 17.5 hour flight to Australia going to compete with those options?
Sure, Australia is a beautiful country and is a great destination for the British particularly. It feels like a home from home in many ways and there are of course over a million British living down under. But, how much inbound tourism will a direct flight really generate that doesn't already travel to Australia via DXB, SIN or HKG etc.?