Accessibility doesn't need another project plan.
Your team already has everything it needs to make better decisions. Better decisions are made closer to where product work happens. I bet you're already doing discovery, planning, design reviews, refinement, QA and release checks. Those moments already shape what you build.
Use them.
The problem is that when accessibility becomes a separate activity and urgent work shows up, as it always does, accessibility will take a back seat. But if you make it part of the work you already do, your team will naturally consider it before decisions become expensive to change.
The last thing you need is another all-hands meeting before every feature. Your existing meetings are enough. Just add an angle to each.
During discovery, ask:
Who might struggle with this?
During design review:
What happens if someone can't see, hear or use a mouse?
During refinement:
What does "done" mean for this?
This way, you make your current process better. And process beats good intentions because process survives when people change teams and when competing priorities naturally show up.