XPS [0] seems to meet these criteria. It supports most of the features of PDF, is an "official" standard, has decent software support (including lots of open source programs), and uses a standard file format (XML). But the tooling is quite a bit worse than it is for PDF, and the file format is still complex enough that redaction would probably be just as hard.

DjVu [1] would be another option. It has really good open source tooling available, but it supports substantially less features than PDF, making it not really suitable as a drop-in replacement. The format is relatively simple though, so redaction should be fairly doable.

TIFF [2] is already occasionally used for government documents, but it's arguably more complex than PDF, so probably not a good choice for this.

[0]: https://en.wikipedia.org/wiki/Open_XML_Paper_Specification

[1]: https://en.wikipedia.org/wiki/DjVu

[2]: https://en.wikipedia.org/wiki/TIFF