Interesting cpp unity build benchmarks!!
created a benchmark that tests a one compilation unit header only unity build vs a regular cpp build (h + cpp in individual compilation units). I really hate writing headers so I prefer to do everything header only. The problem with header only is that every file gets rebuilt every time. This increases built times and becomes a chore. I thought maybe a unity build would offset the time it takes to compile "everything" every time. The results show that a unity build even on header only source code reduced build time by a factor of 6 or 7.
I got pretty extensive in my testing. At one point I created a benchmark for a 1 mil LOC unity header only project and I was impressed to see it built in about 10 seconds. I didnt even try a full build of that for a regular cpp structure (cpp + header being compiled individually) lol. However; incremental builds for a regular cpp structure still beat most unity builds by a few seconds (depending on project size). This goes to show that header only unity builds are fast enough to avoid writing header (declaration) files all together! So if you cant wait until the modules finally get released, unity builds are definitely do-able as they are almost as speedy as incremental builds.