I can't be bothered to update the numbers below as I have lost interest. It is clear that there are somethings that will only ever be available to US developers and there are no plans to change that situation.
December 2016, it sounds like the distant past, but that is how long it has been.
The Built-in Library was released in the US as a "Developer Preview" over TWO YEARS ago.
Only US English Skills can use the 145 Intents
Rest of World gets the standard 22
"Reach wider audiences"
There is lots of news about Amazon releasing the Echo in more and more countries, and supporting more languages. The big idea being developers can reach wider audiences etc
These are two quotes from the same article talking about the Australia/New Zealand launch
This will open up new opportunities for developers in Australia, New Zealand, and worldwide to build for Alexa and reach customers through voice-first experiences using the Alexa Skills Kit (ASK) and the Alexa Voice Service (AVS). Starting today, developers can build experiences for customers in Australia and New Zealand using the Alexa Skills Kit.
If you’re already an Alexa developer and want to target new customers in Australia and New Zealand, you can enhance your existing skill by extending support for the new language model English (Australia) by following these simple steps.
Sounds great? But as far as I can see, this is not true.
Skills made using any of the 145 Built-in Intents will not work outside of US English without significant amounts of effort required to write "work arounds" for each Intent.
Hardly as simple as selecting the correct language in the Skill Configuration page.
(and I won't even go into the Literal Slot type issue)
Existing US Skills will not get rewritten
New developers get put off
Anyone looking to get into developing a Skill will read about the Built-ins in the official docs and tutorials as if they are features available to them (often the US only requirement is hidden away if mentioned at all), when they learn they can't use these features they are put off developing at all with a "what's the point" attitude, or will "wait and see" if they will ever get access.
I don't see how this can be a simple "localisation" issue (dealing with translating languages, differing accents etc).
It can not possibly take over a year to convert something in US English over to UK English.
And if it does take this long and Amazon have been working on it for over a year to implement the US/UK differences, then what hope is there for India English? Let alone full translations for DE and Japan.
Is the Built-in Library going to be dropped?
It's been in Developer Preview for over a year with no changes, there has not been any indication that it is still being worked on.
Is it something we need to worry about?
Will it get replaced by something new, and will the something new work in all territories? Even it that is the case, US will still be able to use the old Built-in Library forever so will not bother converting their Skills over.
This is what happened with the Literal Slot type, it was going to be depreciated, as such UK/DE never had access as it was "old tech" when Echo was launched in these countries.
Then Amazon changed their mind, allowed US to continue using it, yet didn't enable it anywhere else.
Whilst Custom Slots are better, by supporting the old methods Amazon give no reason for a developer to make their Skill compatible, and therefore it will be incompatible with the rest of the world.