I find it incredible that the Telemedia Act, as enacted, claimed to be an implementation of Directive 2000/31/EC - the e-commerce directive - and yet appears to primarily be in use as a method of rent-seeking by unscrupulous individuals. The scope of the Directive (and thus the intended scope of implementing laws) is on the sale and supply of goods and services in the online sphere.
Secondly, and having said the above, I still do not agree with your initial contention. It is my opinion that the hugely restrictive German definition of personal and household activity (doubtless emanating from the critical overreach of the Telemedia and the Abmahnung) is not one which has any reasonable prospect of being adopted widely by other DPAs or by the ECJ. The ECJ has given no support to the idea that website takes on the characteristics of a commercial activity merely by being related to the site-owners profession. Nor has the ECJ given any support to the idea that merely publishing to a publicly-accessible website would be beyond the boundaries of what is considered “personal”; if this were the case, then why provide a personal activity exemption at all?
I agree with Daniel's assessment of the GDPR and how it applies to personal websites. The German interpretation of the GDPR is too restrictive and in my opinion, most likely unenforceable.