We've actually had a few teams at YC using Bubble, either to get in or after, once they were in the program. It's awesome as it's a great validation for our technology.
Not really, as long as it’s a data driven app (and not a platform game...). About half of our paying users build startup-type, customer-facing products, while the other half is small businesses building internal management tools (like invoicing, custom CRM, etc).
Yes, this distinction will probably remain, but we're trying to push where we need to get back to textual languages. If you need to build a machine learning algorithm, I'm not sure visual tools will ever be the way to go (though i'd love to see this).
But both ways work well together. In Bubble, you'd build your optimization algorithm as a plugin, and then you (and even better, others, non technical colleagues) will be able to use the action you've built visually. The Bubble interface becomes the common language between business, product people and coders.