I'm going against the grain, and suggesting you stay with the Nook ST. Not because of B&N's possible future viability, but because 1) you already have a library with B&N currently, and 2) the Nook ST is an Android device at its very core, which means you can
do things if you feel inclined to void the warranty and possibly break the law.
It's technically not legal currently to root an e-book reader in the United States, but in the
past before the newer DMCA changes, I
used to have a Nook ST that ran everything... after rooting, I could use the Overdrive e-book reader, Kindle for Android, Google Play Books,
FBReader, EzPDF reader, I could read RSS feeds, could run Dropbox, and even did email with K9mail and browsed the interbutts with Opera... and I
still had access to the native Nook reader. Even replaced the home screen with ReLaunch.
You can start to fall down the rabbit hole of potential
here. The most useful thing over there currently is probably the 1337 ROM listed
here.
It's that or just buy an
Onyx Boox, which is just an open standards Android tablet with an e-ink display... which will do everything the Nook can (including access to your B&N ebook purchases using the Nook for Android app) without the need for hacking and being a scofflaw. You'll only find reasonable prices through
Ebay, though.
Have fun!