Yes, it would be possible to do so - it would be a simple matter of writing a process that invoked the appropriate Conduit REST APIs to create the articles, comments and links to authors/users from your data export.  The one thing that might be tricky would be the user password property, which would be required for a user to log in and view/edit their own articles, and to follow other users and/or favourite their articles.

That depends on your definition of "REST API on the Intersystems IRIS side".  That Intersystems IRIS provides the HTTP interface?  and/or the code that does the work of the API is within IRIS and therefore ObjectScript?  As far as QEWD is concerned, Intersystems IRIS is simply a persistent JSON store with no other role (though you still can invoke ObjectScript methods and access classes if you want), so a REST API is implemented in JavaScript and handled by Node.js/QEWD.  

These APIs appear to be synchronous, and therefore will not be usable in a standard production Node.js environment where all concurrent users coexist in the same physical process.

This is precisely the reason why QEWD was created - ie to allow the safe use of synchronous APIs, but, then again, if you use QEWD, you won't need or use the APIs described here

Take a look at QEWD:

This is a good place to start: https://github.com/robtweed/qewd-baseline
There are instructions on how to try it out with IRIS, but Cache is also supported (all versions)

Both REST APIs and interactive browser-base applications (and Native Mobile apps also) can be quickly and easily developed.  Security is built-in and it's all Open Source.

QEWD main repository: https://github.com/robtweed/qewd

See also QEWD-JSdb: https://github.com/robtweed/qewd-jsdb

An update: the QEWD-baseline repository now also includes a fully-detailed tutorial on creating interactive, WebSocket-based browser applications

If you want a very rapid way to develop your IRIS applications using WebSockets, and where all your logic is written in JavaScript, and where your IRIS data is accessed as QEWD-JSdb multi-model persistent objects, this is the place to look.

For more info see:

https://github.com/robtweed/qewd-baseline
and specifically:

https://github.com/robtweed/qewd-baseline/blob/master/INTERACTIVE.md
 

By the way, the same techniques can be applied to Native Mobile application development

I guess I'd summarise the "so what?" about QEWD-JSdb as follows:

 The "conventional" approach to database thinking is that your data is "over there" somewhere in some strange and alien technology called a "database", which also forces a particular type of data model on you and via APIs or protocols you have to learn.  It tends to result in two types of developers: application developers who know a language, eg Node.js/JavaScript and build application logic,; and database developers who understand the black arts of data management but don't get their hands dirty with application development.

The key concept in QEWD-JSdb is that the underlying IRIS database is accessed as JavaScript Objects that happen to be on disk rather than in-memory, and can be modelled how I, the developer, wants to handle it - which may differ depending on how I want to deal with the same data. There's no "database", just JavaScript objects that happen to persist in IRIS by means that I neither know nor care about.  

That kind of concept may ring a bell with some older IRIS developers, but to a modern audience it's potentially mind-bending, radical stuff.  Perhaps so, but QEWD-JSdb now makes it possible in a modern Node.js / JavaScript setting.

I suspect, also, for many developers new to IRIS, it will demonstrate ways of using its underlying physical storage that they never realised were possible.

If that's piqued your interest and you have 5 minutes spare, that's literally all it will take to have it up and running and ready to play with.  The browser-based viewer application will give you a real-time view of the IRIS database items you're playing with and how they change as you use QEWD-JSdb, so it's all "instant gratification!" and lots of (hopefully jaw-dropping) fun. 

Just the thing for long, dark winter evenings by the fire-side :-)