That prompted me to look for polls.
> (2015-10-15) 56% of those polled would support a speed limit of 150 km/h on all German Autobahnen
Representative survey by YouGov, source: http://www.faz.net/aktuell/politik/inland/umfrage-mehrheit-d...
> (2018-01-26) A slim majority of Germans (52%) supports a general speed limit of 130 km/h.
Representative survey by Forsa, source: https://www.tz.de/auto/tempolimit-autobahn-knappe-mehrheit-d...
> (date unclear) "Are you for or against a general speed limit of 120 km/h?" - 35% for, 62% against
Source: https://de.statista.com/statistik/daten/studie/258757/umfrag... (they won't disclose source, survey method or date unless you cough up your personal data)
So it appears that a speed limit would be supported by the majority if it starts out reasonably high. (That's the same way the Swiss did it: They started with a relatively high speed limit, and then lowered it as the majority mindset shifted towards higher energy efficiency.)
On the other hand, German carmakers have a longstanding gentleman‘s agreement to electronically limit their cars to 250 km/h. Seems they can live with limits.