Some wishful thinking here. Cats and foxes are way smarter and more agile than devils. Much of the devil diet is carrion not quick moving prey. I'm fairly confident the number of live foxes in Tasmania is 0.

I'd have reservations about spreading dingoes - at present, wild dogs have a massive impact on rural pursuits and native populations throughout numerous areas in Australia.
Granted, these are interbred dingo-domestic feral animals, however with the dingoes there inevitably would be further interbreeding.

Taswegian

I thought that foxes in Tasmania were about to go out of all control. You say that is not so. Please elaborate. I would love you to be correct.

To cover both posts:
Devils are believed to impact upon fox and cat numbers by preying upon juveniles in dens. By effectively preying upon the young, the population growth rate can be kept at or near zero. It is also known that whilst adult devils are predominantly scavengers, juveniles will quite happily hunt for live prey, being much more agile than adults.
On Dingoes, the main problem has been the persecution of animals which results in a breakdown of the social structure. This is when dogs are let in to breed with the pack (the dominant animals being killed by baits and no longer controlling the pack breeding). It is also well documented that where Dingoes have been left alone (such as in cattle fattening country where the predators impose little threat) that there are disproportionately higher abundances of native mammal fauna (especially 0.5 - 5kg range) and very low numbers of foxes and cats. If we can begin to have targeted relases of dingoes, control foxes, cats and wild dogs as well as working with landholders to educate and assist (its actually cheaper to compensate farmers for loss of stock than to conduct massive annual control programs!) then we are well on the way to restore 'natural' biodiversity.