The plugin violates Streamlink's plugin rules, so now that it's fully broken and considering that a re-implementation is not trivial (I just spent 20 mins looking at it), it's finally time to remove it.
$ ./script/test-plugin-urls.py radionet
:: http://deutschlandfunk.radio.de/
!! No streams found
:: http://franceinfo.radio.fr/
!! No streams found
:: http://oe1.radio.at/
!! No streams found
:: http://program1jedynka.radio.pl/
!! No streams found
:: http://radioparadise.radio.net/
!! No streams found
:: http://rairadiouno.radio.it/
!! No streams found
:: http://rneradionacional.radio.es/
!! No streams found
:: http://rtpantena1983fm.radio.pt/
!! No streams found
:: http://sverigesp1.radio.se/
!! No streams found
:: https://drp1bagklog.radio.dk/
!! Error while fetching streams