@mikelove ,
I want to point to only one thing - a native helper for Pleco DB is a much simpler thing than whole app development.
And it requires no future development until DB formal will be changed (i.e. code-and-forget).
For Android and iOS these helpers are already ready
Today's JS-runtimes are very fast and used even on back-end (as it compiled to binaries anyway).
And Pleco is not a multi-user app that does complex operations in a real-time, so surely it will have no perfomance difference noticeable in any way.
The native app already has the data on a user side, so reverse-engineering is just the question of "easier or harder", not the question of possibility.
Sure, there is a good solution (depending on you current implementation) that will help to make a web-version not less secure than current native app.
Why do I think that Pleco for the Web is a promising solution ?
Well, it could be a very long discussion about pros and cons, but I want to point out some pros.
You already mentioned some good examples, just want to note that not only web-services and access-almost-everywhere are great things of the web, but web apps nature itself, as they're the most universal apps.
If you develop both online and offline web solutions - your app has no limits when and where one can use it.
Any OSes will do, even in case of a future OS - when it comes to masses it certainly will have a web browser, based on one of the most popular engine (Blink/WebKit?) and it means that your app is already works on a new platform!
There are some thing that will require native helpers (Screen Reader/OCR, some UX improvement things, etc.) but core functionality (dicts and flashcards) will already work.
At least online.
For core functionality offline support you'll need just add a Pleco DB native proxy app (or just have ready JS-based engine), but even without it online acces is ready.
But the main thing is development cost and time.
What is better - to create many apps for every platform or polish just one universal app, that could work online and offline on any platform?
The answer is obvious.
You'll have fully-shared code for any platform.
You can concentrate on the app functionality and not to fight with every OS/OS versions and device's bugs.
New functionalities/updates will be ready for every OS in the same moment and users have no wait until you make the app ready for there preferred OS.
All development time you can spend on real app improvements, not to make the app just work on other platform - it means users will have better app, faster delivery of new/updated functionality and Pleco will grow faster.
Etc....
I think the main point is clear
It's not so easy as it sounds, but is worth efforts.