"TZDB natural default" is likely to confuse them. Phrase things without using TZDB; for example:
"all year, many people would naturally call France's new time zone "Eastern European Time (EET)" due to the long association ..."
I disagree - if they were aware that France was being referred to, *people* (at least those people with the slightest awareness of European geography) would not naturally do this, given that France is quite clearly not in the eastern part of Europe! Non-updated computer systems, on the other hand, might well associate UTC+02 with EET by default.
For best results, the document should also keep track of changes to civil time in EEA countries, membership candidates, potential candidates, Schengen area, and other countries not in the EU that decide to make a related change. This document would be purely informative, with no authority behind it.
I'd change "EEA" to "EEA/EFTA" so as to include Switzerland. The terms used by the EU are "candidate countries" (not "membership candidates") and "potential candidates". I don't see the relevance of "Schengen area" - all current and potential Schengen area countries are either EU or EEA/EFTA members. And of course the future status of the UK with regard to all of these entities is unknown at present, though in all eventualities it will at least be covered by "other countries not in the EU" - unless it backs out of Brexit at the last minute, in which case it would remain a member state :-) -- John