Not a Nook series 4 owner, but I've owned three Nooks and am currently using the Glowlight Plus 7.8. I can't resist tossing in my two cents.
1. I occasionally purchase Nook books, primarily when I have a B&N gift card. Buying eBooks really isn't a thing for me. I don't need to own them; the library is perfect for me since I rarely read a book a second time.
2. Space doesn't matter to me as I only load a few books at a time.
3. Never used Read in Store, so I don't miss it. But I'm surprised to hear it was discontinued this month.
4. I love the Nook's ergonomics! Buttons on both sides are a bonus (asymmetrical designs bug me for some reason), but the sheer comfort of the Nook in my hand for prolonged periods of time is exceptional. I don't use Nooks as Android devices, load other software or root them, so those aspects don't apply to me.
5. It doesn't interest me, but I see a subscription plan being a good thing to offer. Hope it's successful for B&N.