the UK cannot be included, because they aren’t a Schengen-member and the EU doesn’t want customs checks on their train lines…
it’s entirely up to the UK what they do with their rails within their borders.
and as was already pointed out:
there already IS a connection between the EU and the UK!!
the new plans are largely for connections between capitals of EU countries and major population centers, both of which already have rail connections in the UK.
so what do you expect the EU to do about the rail network in the UK?