I'm quoting @Brendan because of this delicious irony: Balsamiq's philosophy of being so easy to use that beginners can pick it up immediately is what makes it the wireframing tool of choice for many seasoned UX professionals.
It's great for performance that Balsamiq is now going native -- although I will miss the smoothness of the Flex-based app
To perhaps echo the sentiments of other posters here, I have so often wished there was a bridge between Mockups and a rich, interactive prototype, or even a finished website / product. Napkee looked promising, but it never worked very well. I still have to go 'back to the start' after the wireframing stage.
These days, I love using FramerJS for hi-fi prototyping -- although it's not for everyone as it involves coding.
Anyway, here is my wish list for potential features / sibling products that I hope you might build:
A Mockups-style app or plugin that is focused on data visualization. In the last few years, much of my design has been focussed on data viz, which is a reflection of the market rather than of me. One of the hidden strengths of Mockups has been that it teaches users about what standard UI components are, and best practices (e.g. radio button lists stacked vertically). These learnings are required even more in the data visualization space, where few understand what the different chart types are, and how to best use them, etc. Some tools exist (e.g. Excel charts, Google Sheets) but they tend to be data-centric, rather than design-centric.
A 'convert to HTML' feature that creates an exact WYSIWYG replica of wireframes in native web pages, but using a series of graphics per page, rather than a single static graphic per page. A further option could be to allow the user to manipulate the web designs in various ways, e.g. to individually convert the graphical elements into native elements, but to roll back if this makes it look wonky. The final output would still be a prototype, not a polished design.
A 'product builder' that is 100% visually focussed, and doesn't aim to teach the user anything about coding or coding concepts. This is hugely ambitious and somewhat of a holy grail. I have some ideas on this, but who knows if they would fly?
If you've read this far, thanks for indulging me