I value compatibility and future reuse very much. For this, I’m really annoyed by Apple’s tendency to abandon compatibility with the older file formats of their own apps. At the same time, I depend very much on their software, so I need a strategy, that can be extended to other brands.
As much as possible, I keep saving a copy of my data in a tested interchange file format, like DOCX, RTF or IDML. In case this is not possible or doesn’t make sense (for example, with Logic Audio), I resave the older files into the newer file format after a few years/versions.
Standard formats may change on the years. Some are standard only on paper – take ODT, for example, that has even an endorsement from the EU, but is not even generally adopted by the EU.
LibreOffice+OpenOffice, while open and free (but good chaps contribute from time to time!) should be not much more widespread than Apple iWork apps, and this may vary depending on places. For example, Pages seems to be very common in the schools in the USA. LibreOffice is in public administration in Germany. The publisher with which I’m currently doing a work makes no difference between Word and Pages (they are Mac based, and in any case anythings ends up in InDesign).
Google, whose apps seem to be now the dominant ones in the business, removed the idea of file entirely. Their apps are in a mysterious format in the cloud. If you want a copy of your documents, you have to choose an interchange file format, most likely DOCX for text documents.
So, in the end, it will be not much different than writing with any app you like, and save a copy for archival in a (de-facto) standard format.
Paolo