• Any xz-tool can of course decompress a tpxz file, though it obviously can't use the index
• Some tools can at least do parallel-decompression, though it's not common. No idea if any such tools are on Windows
• As far as I'm aware, nothing aside from pixz itself shares our index format. But you should be able to compile pixz on Windows, or at least in WSL

Thanks for the quick reply. Sometimes I need to GUI browse a large archive and it's always painful to fully extract it before 7-Zip or WinRar will let you browse it, then do it again to extract any files. Here's hoping 7-Zip add support!