Why exposing RCS-e/joyn telco enabler as UNI API?

We are being asked about why exposing the telco enablers as UNI (user to network interface) API. Telcos need to understand the advantage of exposing their assets from the end-point point of view.
There are several reasons:

Avoid lock-in: if you expose the capabilities based directly on IMS and/or instant messaging server interfaces, some propietary shortcuts (and "optimizations") would be introduced and thus create lock-in. This forces that both core and API has to be provided by the same vendor and will be difficult to replace.

Security: when exposing RCS-e as end-point (virtual client) the user of the API can only do the same actions that a phone will do, no more. And subject to exactly the same security enforcement checks.

If the API application is behaving not properly, just removing the "user identity" of the application from the core using the same procedure as with a phone is enough.

Remember, in this way of exposure, the API and solutions using it are outside the SBC and then formally outside the network. Developers would be trusted as a phone would, with no extra security invesment over having the same number of "normal" users.

OSS/BSS savings: provisioning, billing, rating, etc. is done re-using the same systems in place for "normal" users. No need to create a different kind of users for applications in vendor-proprietary systems with a huge OSS/BSS investment. With UNI exposure an application uses an RCS-e user created in the same way as a "normal" user.

Cloud-based exposure: with UNI-based exposure, telcos can keep core (IMS, IM server) at their premises and adopt cloud based API exposure. Benefits: OPEX savings; shorter times to scale the API according to the usage requirements; possibility of offering the same API to several opcos or even resell to other operators, etc.

Standard compliance and testing: when RCS-e is exposed to 3rd parties as an UNI API, it behaves as client, there are no dependencies on what's inside the network. Once the API based virtual client interoperates with the device clients in the market it is clear that your API exposure will be allowing to create 100% RCS-e/joyn compatible solution on top.

For those reason Solaiemes pioneered the UNI approach to expose RCS :-)
Feedback welcomed.