Getting acceptance for new document formats from users is difficult. If someone gets a file with an ODF or some other extension they have never heard of it will be a worry for them. But if they get a PDF file that is okay.
Perhaps PDF can be used as Trojan horse (in a nice way) for this. Some versions of PDF (such as PDF/UA) have provision for embedding data files. This could be used to include a Open Document Format (ODF) or web document and its associated formatting and images inside the PDF document.
The OpenOffice.org office suite could be modified to package an editable version of documents in a PDF file (and an equivalent addon provided for Microsoft Office). OO already creates PDF versions of documents, so to this could be added an option to include a copy of the original source document. The person receiving the document would see the PDF rendering by default, but would have the option to work on the original editable file and be offered a link to download a copy of OO, or a conversion tool for Microsoft Office, if needed.
Most of the space taken up by word processing documents is in the images, not the text. It should be possible to share the images between the PDF rendering and the ODF document. As a result adding the ODF document to the PDF may not make the document much bigger.
ODF is better than not having a standard format for office documents, but is not perfect. My preference would be to use XHTML 2 for word processing documents, so they could be directly rendered by web browsers. Word Processing programs are rapidly becoming just a way to create not very good web content and it would be better if they created well formatted web format documents directly.
Compatibility with existing products is a legitimate concern when setting a standard. As an example this was a major consideration in the standard for shipping containers, with discussion of what adaptors would be needed.
Standards based on something which has been shown to work are better standards. But this does result in some quirks, as an example shipping containers are stronger than they need to be (increasing costs) due to the need to meet some old European railway standards. The cords for some computers are rated to withstand high temperatures as the standard they are made to was designed for electric kettles. Putting office documents inside PDF files would be a bit like a computer cable you could use to boil water, but at least it would work.