The quickest way of modernizing your application build on Notes is probably by keeping it on that sublime application platform and provide a new user-interface and updated business logic to it.
As a demonstratable example I would like to bring up my own Bildr project on OpenNTF.
A brief history
The application started initially as a web browser display only and create content via the Notes client application in the early 2000’s. From that the application was updated in a create content via the web browser too features.
Later the oneUI was implemented in a later step also utilizing the Application Layout control. With the Bootstrap4XPages plugin a responsive UI could be delivered a couple of years ago.
Nowadays the Application Layout control is no longer used but the Bootstrap responsive features and components are used further through the application.
The application still relies on XPages and Notes data (allthough used mainly in JSON format). The business logic resides mainly in Java Classes. With the separation of design and data the application could be hosted on Bluemix (not tested, please do).
Looking back at this application story I believe the application will change also in the future (or die) perhaps a challenge could be to have the data optional in a different source (e.g. MongoDB) or exchange XPages for Angular and run it on Node.js.
So if you have experience moving data from Notes to MongoDb, applying a similar ACL and Roles security model on your application I would be happy to hear your experiences.
Or if you are still on the Notes client only level and want to bring your application to a (mobile) browser I am happy to exchange ideas with you and learn from your situation.
Why am I saying this? Today I uploaded a new version on OpenNTF and for many Notes developers who a) not have taken the XPages path yet b) unfamiliar with Java and JSON the application could be a great starter example.
Lately there are not that many (new, updated) projects (applications) available at OpenNTF so the chance to find a working demo to see and understand the code and data running are a bit scarce (I am sorry).
I remember in the days of Superhuman Software a quote about Notes and collaboration was “dare to share” so I would challenge more developers to do so. We can learn a lot from examples from others and I thank those people who (still) do and from which I can learn from!
I wish you a wonderful learning experience at IBMConnect 2016!