How to do it manually as a foundational exercise; and how to implement it using a popular gem.
Users have high expectations for search functionality these days and it is commonly at the heart of most modern applications. How do the pros do it?

How to test Javascript functionality in your Rails app.

testing the whole stack!

Especially in the context of Heroku, Postgres, OpenRedis, Unicorn, Foreman & Sidekiq. I'm sick of the time-out errors etc and I'm sure many others are too.

Rspec 3 have some syntax changes and configs, show us the news!

Anyone have a better idea.
My app https://github.com/mysmaily/Blog-posts

I have tried twice to use vim because I see everyone saying to give it a go but the hurdles to setting it up scare me off. I don't mind sublime text but when I saw your videos and how you command vim I found I was learning differently than I had done before.

If you could show how you think a beginner to rails could setup vim so it works as intended (ie vim-rails, vim with git, vim and rspec plugins etc) that would be awesome.

For instance how to test that an image is successfully stored on Amazon S3

http://rubyonrails.org/screencasts/

Setting up FB and linkedin log-in etc.

You've discussed authentication with Devise do you think your next video could be on authentication maybe with CanCanCan, Pundit or Authorize?

http://rack.github.io/

Twitter, Facebook, and plenty of other sites are parsing out @ and # symbols to add a huge amount of flexiblity to their applications with minimal UI attached to it. It would be fantastic to talk about how this can be done in your own applications.

Walk through GoRails itself

Some sort of profiling tools, e.x. ruby-proof

How do drag and drop builders work? Let's make one!

How to correctly use JWT? Imagine Rails API with a JS frontend (e.g. reactjs). How to make it secure? How to handle expiration? How not to use it?