SonarSource has said that they would be dropping support for Ruby on Rails. So assuming that we would need to use Web APIs from here onwards, what are alternate ways of writing your widgets? Has anyone tried any alternate ways of writing one? And how do you link said widget to the UI?
Short answer:
In upcoming versions of SonarQube, widgets and customizable dashboards will be progressively be removed. You will still be able to use the Web APIs to get all the data you want but you won't be able to contribute changes to the "dashboards" of the product.
Long answer:
SonarQube was initially designed to be able to inject and display any kind of information, mostly thanks to the customizable dashboards and widgets (that are indeed written in Ruby). While this helped getting widespread, the downside is that people started using it as a multi-purpose aggregator and reporting tool. One would add information coming from a bug tracker system, another one would add documentation information about projects, ...etc. The consequence is that soon, the global and project dashboards ended up being full of useless and useful information, everything mixed up together in a big mess.
So something had to be done to get back to what SonarQube is meant for: managing source code quality. Every information that can't be precisely linked to a source file should not end in SonarQube. Having said this, it becomes obvious that having a mechanism to define custom dashboards and widgets is just too generic. The web application must provide features that answer precise needs for a precise audience. This is why customizable global and project dashboards are progressively replaced by "hard-coded" pages which answer those use cases. This started with the new project home page introduced in the 5.x series of SonarQube and available in the latest 5.6 LTS. And we'll do the same with global dashboards in the 6.x series.