Would it be possible to get to audacious from 6 illustrious class
No need for six Illustrious. You go from 3xIllustrious, 1xIndomitable to four planned Audacious class. There’s nothing innovative in the Audacious, other than a return to the twin full length hangar that the 3xOutrageous and Ark Royal 91 had.
The only challenge to getting at minimum the first two if not all four Audacious completed in time for late WW2 service (same as IOTL Implacables) is to overcome any treaty obligations and limitations on funding, materials, labour and yard capacity. Same as with any large warship. To get there by freeing up attention and treasure, we forgo the 2xImplacables, and entirely skip the 6/8xCentaur (1st unit laid down 5/44) 10xColossus (1st laid down 6/42) and 6xMajestic class (1st laid down 5/43), and maybe HMS Unicorn (Audacious are big enough to do their own repairs). And don’t let those 22-24 CVL’s civilian spec and yard use distract you, it’s still men, money and materials to build those two dozen light carriers, that could be better used for expediting the four Audacious class.
And thus WW2 closes with the RN having ten armoured fleet carriers, including the four Audacious, plus dozens of escort carriers. Postwar the 3xIllustrious class, Indomitable, Furious and all the CVEs are soon disposed of. Once that’s done, two Audacious are on active fixed wing service, another serves in a rotary Commando role, the fourth is in reserve. Until the Korean War, when two Audacious configured for fixed wing strike deploy to Singapore, and the other two are back to fixed wing strike and fleet air defence for NATO in the North Atlantic.
Post Korean War, we get moving on the Malta class.