My .02: I disagree (to a point). I am not a 'developer' but am probably a 'power user'. I've worked with the product since 3.0, have rudimentary JS skills, and have personally designed, deployed and supported our 6 different deployments, as well as helped some of our customers (we are a partner - I am the CEO).
I previously had a CRM developer on staff and we were a Dynamics CRM partner (I held some of the role requirements) until it didn't make sense to maintain one, or that partner status, since we did not have much success selling the product in the 3 and 4 days.
That said, I know enough to know how to implement the controls, and use the SDK up to a point, but I am still the CEO of my company (an MSP) and that is my primary duty. We are a small business and cannot justify paying up to $100-$200K for a 'developer' to do work, much that I can do myself, only to find that i have to recreate that wheel each time the product is upgraded and MS decides to make major architectural changes. Granted, 4 to 2011 was the most painful but the deprecation of DOM support also caused headaches.
For the things beyond my skillset, I subcontract. But I still don't think that should mean that custom controls should be made available for everyone *BUT* web clients, which I'm pretty sure are the bulk of the installed user base, and I still do not understand what MS is thinking or what their strategy is on this issue because they've done a poor job of communicating this stuff publicly. And if they have, that is, again, the whole point if this post and why I asked.
I also disagree that customizing the product should be treated like some black art, only within reach of 'developers'. MS wants to beat SalesForce and dominate the market and that means that they have to put the product's customization features within reach of more users - more than JUST developers. They seem to be doing a much better job of that with their cloud offerings than their on-prem but the fact is, cloud is not the right solution for every deployment and the elephant in the room with cloud is last mile connectivity (aside from the fact that MS and others have proven that they cannot be trusted to protect customer data from the NSA, etc - but that's a different issue entirely). MS needs to provide functionality for on-prem users that is on par with, or at least much closer to what they provide for cloud if they want to keep accelerating their adoption rates because it is a fact that not everyone is as enamored with cloud as MS is.
My only hope and expectation is that MS provide functionality for on-prem that is on par with what they provide for their cloud offerings, and when they cannot, they make their plans much clearer than they do on these pages, which leave many questions unanswered:
https://roadmap.dynamics.com/
www.microsoft.com/.../get-ready-for-the-next-release.aspx