From my own experience, to stop on the audiophile road has more to do with your financial resources and how you are satisfied (or not) with your current gear.

And if we're considering there's not always a proper upgrade for what you seek, you might end up with several systems, which is more easy to do with headphones/IEM compared to speakers.

Overall you could ditch your Sundara for a pair of Arya which provides better resolution. It's not bad by any means, it does make sense you'd want them if you had a good experience with your Sundara.

If say you choose the Arya you could stop it there (openback-wise) as the Arya is well known to be an all rounder in this high end segment. Now if you don't have any budget limitation whatsoever why not just get the Susvara and be done?

Another thing to consider is how often do you use open back headphones in your daily life? If you're using most of the time your speakers at home, maybe there's no need for you to consider buying new headphones. Basically you need to brainstorm that and think of what gear will address your needs. And i wish i did that earlier as i have active speakers, 4 open back, 1 closed back and 1 IEM in my collection.

Hope that will help you in some way.