" So what you are requesting is that when you specify "output.jpg" and that file already exists, the output is written into output0001.jpg? "
yes, sorry for late response - thought you have enough info.
the issue is that when rendering 5th frame for example, it will not add padding (name.frameNumber = framename.0005) - that prevents rendering sequences using scenes exported to corona standalone scenes. i only submitted it becasue it's the standard option with vray,arnold and all others. using standalones helps to resolve certain issues and also allows one to render his animation faster, so that would be a prett yneat feature.
PS
haven't got time to fully test corona, but from my renderfarming experience (i'm the troubleshooter) i must say it behaves great! (compared to vray for example, arnold also has more issues :) )