Definitely agree with your principle.
But I'd take slight exception to your implicit assertion that HTML is a suitable standard for long-term access and archival - it's way too browser-specific these days. At least with XML or something similar, it's feasible to then transform the underlying structured data into something readable/meaningful for a particular audience/platform.
(disclaimer: I spent a couple of years working on a UK/european project that was trying to scope out the whole "digital preservation" can of worms - XML was kinda forced on to us when it was still a standard in development, so this stuff left a scar
)
That said, if we're talking transparency, cost-effectiveness, efficiency... SOME form of open standards are the only way to go.
(IIRC, didn't PDF become an open standard not so long ago? Pretty sure Adobe opened it up - which is a good move, cos at least a de facto publishing standard is now wide open. Of course, there's the side issue of just how many PDF docs are actually well-structured and well-formed in their own right...)
It's a great chance for Hamilton to take a lead in something that I strongly believe will become the norm in the long run. So why not lead early and excel from the get-go?