This isn't a WordPress site that we can just slap together in a day, however, and the new platform is internally a completely different beast from the old; there are a plethora of subsystems and details to consider, so the process hasn't been as straightforward as you seem to be implying.
At work, I'm currently on a project with 3 other guys, and in 3 months we've gone from having nothing to having a usable web-based product that's we're not only using in our own business, but also already selling (as SaaS) to other businesses in our industry. Just in the last week alone we've added a new major feature that's roughly as complex as CurseForge's ticket tracker. If you exclude the packager and repositories, I'd estimate the two systems are about equal in total complexity, and you said those were finished ages ago.
On the other hand, Curse has done this -- exactly this -- before, and presumably has full-time employees who aren't learning on the job. It just should not take this long.
...Though frankly, considering what I've seen of the beta site, I kind of hope it takes forever because I really don't want to have to use the new site. :(
This sounds miserable, as no GUI client for Git I've ever seen has this functionality -- they all just "push tags". If I wanted to type crap on the command line all the time, I'd use Linux. My first several computers ran DOS, and I don't see why anyone would voluntarily go back to that for basic everyday functionality. :p
I will say that TortoiseGit (which is what everyone uses on our Windows dev boxes at work) has a 3-state checkbox for tags on pushes, as well.
Git for Windows installs MINGW (which is like Cygwin lite) as part of its install (it calls it "Git Bash"). I use ConEmu to run MINGW and do all my gitty stuff from there (Git for Windows also installs a lighter terminal replacement which is functional). I do have Tortoise installed at work, though, because an interactive Git log viewer is a million times better than anything you can do on the command line.