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.
On the scholarly front, the use of BibLaTeX is a significant step forward re: BibTeX.