Save As feature was discussed several times in the past. A project is made of many files, not a single file. A proper Save As feature will need to do something with all the files.
I think that the Export as zip provides a better solution.
'Export as zip' is fine for making backups, but occasionally I might make a mod that I suspect could break my code or just an optimisation to some working code. With this I usually like to 'save as' which allows me to open both projects and compare differences. If the change doesn't go as planned. The 'export as zip' still works for me in so much as I just unzip to a different folder and rename it so that I can have both projects open at the same time.