Not GP, but for me two of the most exciting things are the UTF-8 ready engines such as LuaLaTeX and XeLaTeX, on one hand; and on the other, the fontspec package and similar ones, allowing LaTeX to seamlessly use system fonts.
On the scholarly front, the use of BibLaTeX is a significant step forward re: BibTeX.
Yup, I totally agree that LuaLaTeX and BibLaTeX are awesome; that was even my platform for the (uncontested) TUG board election [0]. But UTF-8 mostly just works with LaTeX these days, regardless of the engine: even pdfLaTeX has defaulted to UTF-8 since 2017 [1]. Fonts are still a mess in pdfTeX though, so I'll definitely second your fontspec+LuaLaTeX recommendation.
- The LaTeX tagging project [0] is definitely the biggest ongoing project, and they've been making really good progress lately [1] [2].
- ar5iv [3] is somewhat outside the TeX world, but I find it pretty interesting since it's able to successfully convert most articles to HTML. Usually conversion tools have either required perfect markup or manual fixes, but ar5iv is completely automatic, and it even works with the horrible programming practices that most document authors use.
- I'm personally a big fan of ConTeXt [4], a lesser-known TeX format. ConTeXt itself isn't new, but it tends to gain new features quicker than the other formats; some recent new features include improved math typesetting [5] and improved paragraph breaking [6] [7].
- The LaTeX Team just published "latex-cmds" [8] a few weeks ago, which is a handy reference to all the recently-introduced macros (and some older ones too).