That's an important issue, but if Democrats ever see power again, it'll be important to focus on re-enfranchisement (RCV, instant runoff, or anything fairer than FPTP; NPVIC; national mail voting; mandatory voting), on judicial reform to undo the corruption and incompetence that has been packed there. Without those, keeping any gains will be impossible.
Then, triaging existential threats is critical, which will mean fighting climate change, investing in public transport (trains), and breaking up trusts will have to be pursued simultaneously. Stopping any support for genocide needs to happen as soon as possible.
There will be plenty more structural changes to fix beyond that: Protecting whistleblowers and protesters, improving FOIA, replacing norms with laws (Emoluments Clause enforcement, financial records disclosure, no insider trading for Congressmembers, &c), and all manner of civil rights protections and police reform.
After all that, it'll be time for the stuff I've been hoping for: nationalizing healthcare and Internet access, and copyright reform.
Adding seats to the court needs to happen, as well as reapportioning representatives, and giving electoral votes to DC and the territories. We need to find politicians that aren't afraid to do it.