As you say, js world is fickle and I wouldn't count on Adonis being here for a long time. Mix and match is more pragmatic in this setting.
Nor can you count on your JS library to survive until next winter.
In Js world it's better to not bet everything on a single horse
Adonis is starting to get there, but I don't know much about the core team and how long they've been working on it. If they are able to focus on delivering core features and not getting distracted by every wave that hits the JS world, eventually the level of convenience they provide will reach a tipping point and developers will flock to it.
- JS libs often target browser as well and that's a fast moving target
- JS is primary language of serverless which is also moving fast
- it attracts younger devs chasing hot trends
- the fragmentation is already there, people got used to it and some even embrace it
I lead development on a 12 year old SPA. It's a Ship of Theseus where there is almost zero original code but we never had to rewrite from scratch, instead we were swapping piece by piece as we went. The time investment was reasonably small and we never endangered the business with the full rewrite. I shudder at possibility that someone before me picked "batteries included" AngularJs (the V1). A sibling project is still fighting it today!
Consider choosing Oracle as your database. It is a great database maintained by a big company so it will be around in future too. But you will be locked-in to very expensive licensing because when big businesses are "locked in" Oracle can and will raise their prices.
Compare that to the wild west that is Javascript land. Multiple libraries that all do the same thing in different ways. Stuff being deprecated or completely changed.
Sure, if you want "choice", there's plenty of stuff out there for that. You can cobble together your own framework or pick a light framework pick and then add your "batteries" to it. I hope AdonisJS only has 1 way of doing things and that those ways are good, then it will truly go a long way.