It is, however, endorsed by some EU department and a bunch of other entities (see bottom)
Some -- not all -- of the other cosigning entities are ridiculous. One of them (Normalzeit Leben) is literally the title of one person's blog where they talk about their struggles with DST.
[1] https://en.wikipedia.org/wiki/European_Economic_and_Social_C...
doubtless, the irish representatives wouldn't support any divergence between Dublin and Belfast, (especially considering this is wrong from a spatial perspective as population density is heavily skewed to the east of the island).
edit: i was curious enough to email all of the irish delegates to this organisation. some fairly heavy hitters, as a citizen with a keen interest in Dublin & Belfast being in the same timezone will be interesting to hear back!