To be honest I think that small updates like a few examples here:
“We should hear from our lawyers in the next few days for the green light ”
“Were getting there ”
"Were now starting the process to integrate Apple Pay! "
"Our last name idea has already been trademarked "
Are great for Twitter and Snapchat as they are small not important updates that not everyone wants to know about. However, I do have to say as soon as big updates (such as like the new name or even were now a bank!) are announced then yes they should be announced in better mediums such as emails and blog posts as they should be told to everyone, not just the people that want smaller updates.
So to simplify:
Small updates - Snapchat, Twitter, Facebook, Instagram maybe
Big updates - Email, Blog post, Article, and more professional and business types of communication
Here is a nice little suggestion to get the updates out there as I know banks like Natwest have just started doing it with their app. Whenever they have an announcement such as downtime or a new feature like Touch ID they show it to you when you open the app and a button to continue to your accounts. This is a great way to send out announcements to everyone that has the apps and you can even make it send a notification to the phone if it’s something really big to get people’s attention.