I'm not sure we'll ever know exactly what is or has gone on behind the scenes between Microsoft/Nokia and Verizon. Everything is speculation.
Certainly one aspect worldwide is the differences in how cellular standards have come about and how at times, being among the earliest to implement such networks isn't necessarily a good thing. That Verizon (and Sprint) in the US still use CDMA instead of transition to GSM is a case in point; it's always been difficult to bring your own devices to networks that simply aren't open. AT&T used TDMA prior to acquiring Cingular, and then beginning a changeover entirely to GSM. It was painful for subscribers at times. But now those subscribers have the benefit of the much more open GSM-based cell phone devices being usable, simply by inserting the SIM card you already have in your current device.
Now today, we certainly have chipsets used in mobile devices that can support all current cellular standards and frequencies. Of course, it seems those same chipsets still have ways of being configured/combined to support subsets, but the option exists to use combinations that truly support everything in use today. At what cost? Certainly at a slightly higher cost, but really, $1, $5? Who really knows, but [probably not a lot of price difference. Of course, 5,000,000+ devices x $1 is still a chunk of change worth saving.
But in the case of Verizon and Sprint, they still have to allow those devices on the network. Unlike GSM where the real identifier is the SIM card, CDMA networks require use of information on the physical device, and that means the networks have much more control over the devices they allow to connect.
Verizon is a hybrid. There's simply no way most could live with the LTE-only side of Verizon. It's the CDMA side that gives them the complete coverage they have. The LTE deployment is comparatively very spotty. Verizon compatible devices simply must support CDMA, and must be allowed onto the network by Verizon.
Would Microsoft create CDMA-compliant devices that can physically connect to the network?
Would Verizon authorize those devices to be usable on the network?
Now until we really see inside the 950 and 950 XL devices, we can't know for sure that support isn't physically there for CDMA. The SoC supports it, but there's other components that must be used on the radio front end, and they could have chosen, for whatever reason, to use one that cannot support CDMA. Or it's there and simply disabled for now.
But of course, to figure this out we need everyone to be more forthcoming in what's going on behind the scenes, and I doubt we're going to ever truly get that.
But keep in mind that it's more likely Verizon wants control over things on their network, and has a stronger reason to put up roadblocks to Microsoft, or anyone else, without some sort of deal. It's much the same in Cable company deployments; it's required government controls to get to a point where third party devices can be used on their networks for cable channel access, but the video-on-demand segment is still a mess, and only TiVo has managed to get a foothold in supporting that on just two of the major cable companies so far.
For the most part, at least, there's more competition in the cellular industry, though of course coverage differences are a practical concern, especially in less populous areas. But it's far better than the state of cable competition. So aside from expressing the desire to Verizon for devices like the 950 and 950 XL, where possible, you may need to give Verizon more incentive: actually switch to using other providers to express that displeasure. But most importantly, whether you stay or switch, you need to let them know you're unhappy with the current state of things, and in this electronic age where sending emails is far too easy to automate, nothing is going to carry more weight than a real, written letter sent via US Mail with a concise explanation of your desire and your unhappiness over the current state of things.
And maybe behind the scenes, there actually is work going on to create CDMA-supporting versions of these devices, but perhaps it involves some amount of give and take on both sides and that's preventing it from being even talked about yet in public. And certainly some external pressure from their customers would be a good thing, too.