I don't think it's ever too late to think about accessibility and improve your product for people who need it.
It just gets more expensive the later you do it.
If you started thinking about accessibility because you got a complaint or you freaked out because of an audit, you might think, well, it's too late now. I hear you! That's okay. But it's not too late and there's no need to freak out. You're here now. And there's lots you can do to improve your situation.
The cost is higher, but you already know that. And you might think you have the comfy alternative of doing nothing. That's your choice. But that's a choice that keeps people out.
Every release cycle you wait is another one where late just gets later. It's not that you won't be able to claw your way back. You will. But why keep adding to the already rising costs?
I'll run a similar scenario by you. Every line of code you write will eventually become legacy code. That's code that eventually no one on your team will know what it does because the person who wrote it is long gone.
Frameworks changed. Technology moved on. Best practices from yesterday are just the status quo people are complaining about today. You're not freaking out you need to update your product every however many months and fix bugs that have lingered there since v1, right? Why should accessibility be any different?
So if you're reading this thinking you've already missed the boat, you haven't. The best time to start was right at the beginning. Now is just as good.