By the 2030 World Cup we will transition to Gauci, Hall, Beach and Dylan Periac-Cullen (unless others appear). Ryan will retire from the national team after the 2027 Asian Cup when he will be 34. Izzo won't make 2030 when he would be 35 so probably should also retire after the 2027 Asian Cup.
In order of potential - not current ability, I would rate them as Dylan PeraiÄ-Cullen, Steven Hall, Joe Gauci then Patrick Beach. Others might appear but so far the rest are well behind where I see these going. In fact, at the moment, the gap after Ryan and Izzo means we have to go to these four and even after them it looks bleak. TBH - potentially all four will be better than Izzo and a couple will push Ryan's best - probably DPC and Hall.