the new law says, that to qualify for benefits in Denmark you must have been living/staying in Denmark OR another EU/EAA country for 7 ouf of the last 12 years. The proposal dont say that you must have WORKED here 7 years.
About the other part of your question: Will I be affected by the new rules, if I join A-kasse now?
Yes, regardless of when you have joined an A-kasse, you will be affected. Everyone who applies for Dagpenge (Unemployment benefits) after January 01, 2019, must meet this new requirement.
Anders Weber, www.a-kasser.dk