IBM and HCL held a webcast today to detail some plans for Notes/Domino V11. There were some interesting tidbits elaborating on things like the pub/sub support, and it'll be worth tracking down a recording of the event when it's available.
What's important for this series, though, is that this event served as the long-promised "roadmap" announcement for XPages. The roadmap is, in effect, option three: HCL plans to look into ways to reuse some existing XPages code, but in general you should be aiming to write your UIs in something else, either consuming REST services from an XPages container or accessing Domino data via another route (like the
domino-db Node.js module and hypothetical Java gRPC client).
So we know the end of the path: not XPages. However, it's not like we're all just going to throw away our existing apps, so there's work to do determining how we're going to get there. The options remain pretty much what they were after CollabSphere last year, albeit now with the doubt removed. The first two options - returning to LotusScript or going to Node - have their advantages and disadvantages, and you could make a reasonable case for either. Personally, I'm not interested in going down those roads, though, and I think it's better for any app of reasonable complexity to dive into Java. Other members of the community and I have developed tools over the years to make it easier, and now's the time to take some of these steps if you haven't already.
Learn Proper Java
Java has been around for a long time, and the way to right "good" Java code has changed over time and varies greatly by your environment. Some aspects, though, apply generally, and it's useful to stay up-to-date on current practices. I don't know a better resource for this than Effective Java, which has been updated for Java 7-9 since I last read it.
Speaking of which, you should learn about Java 8 streams and lambdas - they're great. Julian Robichaux did a presentation on this topic back at Connect 2017, and the slide deck is very elucidating.
Adopt Standard Java Technologies
Last year, I created a project to bring some modern JEE technologies to XPages. These are some of the same technologies I've been talking about in my "XPages to Java EE" series and, while that project can't bring the full JEE development experience to XPages, using those tools will help you write code that, in some cases, could be directly dropped into a Java EE app with no modifications at all. There's a big asterisk when it comes to actually accessing Domino data, but that's a solvable problem as well (with some more development).
In particular, you should start writing JAX-RS services. Not only is JAX-RS an excellent and very-capable spec, but REST services are portable to absolutely any front end.
Adopt Automated Builds
Maven has been something of a bugaboo for XPages developers for a while, but doesn't have to be. Node development (server- or client-side) revolves around npm and various build plugins, and Maven is much the same thing. One of the biggest improvements I've made lately to all of my active XPages apps is to wrap the on-disk project for them inside a Maven artifact, using the NSF ODP Tooling. That project allows you to automatically build your NSFs alongside other parts of the project (such as OSGi plugins) without having Designer involved.
Check the example project in that repo, and stay tuned for a 2.0 release (probably) imminently.
Learn Other Toolkits
If you're just starting the process of figuring out what to do after XPages, it doesn't particularly matter which other toolkit you learn, as long as it's reasonably modern. If you take some time to learn how to make, say, a React app but end up going with something else down the line, the lessons you learn will apply very closely. A particularly-comfortable option could be to learn JSF, which has a common ancestry with XPages but has up-to-date capabilities.
Whatever it is, though, just learn some other toolkit.
Follow Channels and Accounts for Other Tech
Over the last couple months, I've started following a lot of Jakarta-related blogs and Twitter luminaries. This applies elsewhere - even if you're not using other toolkits yet, it's very helpful to start immersing yourself in the news and culture.
Don't Stay Still
The primary thing to take to heart is the importance of doing something. Unless you're planning to change careers or retire in the short term, you'll have to make one decision or another. XPages is not going to get meaningfully better, and even existing apps will get worse with time as browsers and technology change.
Other environments, though, are already leagues ahead and are constantly improving. Dive in; the water's fine!