@RobertMyles if it's general web development you're interested in learning, Shiny is maybe not the best vehicle for doing that. Shiny's architecture is quite different than other web frameworks, so you'd have a lot to unlearn if you want to take your Shiny skills and apply them to, say, a Django or Rails back-end.
That said, IMHO general purpose web back-ends are not all that interesting these days for "modern" web apps--all the complexity and interesting bits have moved to the client side with things like React, Redux, and d3, while the web framework mostly speaks JSON. Anecdotally it feels like many people are finding they don't need heavyweight web backend frameworks and are just using lower-level web frameworks like Flask and Express. If you learn those techniques and want to apply them in R, you can look at httpuv, fiery, plumber, OpenCPU, etc.