The only thing missing is an option that you could claim a swap space as designated for only allowing tmpfs spillover.
Most of our servers have small amounts of swap and aggressive overcommit_memory settings. The small amount of swap makes is enough for the incidental extra memory needs and can be helpfull on loaded servers for accumulating effectively wasted memory.
But we do often generate lots of temporary files (for sorting or graphing) and some might actually be rather large. But if it means that I have to increase the global swap space than that's really no option.
I know adding swapspace and tweaking the overcommit_memory_ratio would work, but I don't want my shared memory in /dev/shm any more swappable than I want the normal anonymous pages (only /tmp tmpfs should be allowed to use the additional swap space)
Tmpfs really is the most sane option for /tmp. Why bother doing cleanups at boot? Why bother guaranteeing on disk-consistency or doing disk flushes on sync/fsync/fdatasync. The only sane alternative would be a ext2 filesystem with all data guarantees turned off and recreating it every time you boot.