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Losing them would be really bad for Microsoft, ...It would be, but they won't lose them.
Those folks aren't going to just all of a sudden stop using or recommending or integrating/deploying Microsoft products. With regard to licenses for development / test / demo machines and such, the 180-day evals (which can be "renewed" for 30 months, IIRC) aren't going away and will work just fine for them in the majority of these cases. Besides, the dev shops and integration businesses aren't who Microsoft is targeting right now -- they provide value to Microsoft and will continue to do so.
There's a lot of "partners" that are only partners because of the money they save in licensing costs. Why would Microsoft really care if they remain partners or cost? Their value to Microsoft is very little (and probably a net negative in many cases) so why not force them to pay "full price" for their licenses too? Microsoft has been effectively giving them away like candy for years and years and now that's going to change. They may have backtracked, for now, but I fully expect them to continue limiting, restricting, or totally phasing out internal use rights -- except, perhaps, for the higher/highest partner levels. To Microsoft, the smaller "partners" just aren't worth dealing with at this point and this is an easy way to get rid of many of them without simply "kicking them out" of the partner program.
I've thought about this a lot deeper than I care to write about here at the moment but I think their long-term goal here is to continue to push as much as they can into Azure for that sweet, sweet (monthly recurring) "subscription" revenue (plus licensing!) month after month. For anything else -- whatever they can't push into Azure (where they can track it much better) -- they're gonna make sure that everything is fully licensed and that they're extracting every penny that they can. They simply don't need the majority of the partners in order to do this.
Microsoft, of course, is after the large enterprise customers -- the ones they can extract the most revenue from. (By the way, they can already work directly with Microsoft Professional Services and "skip over" the partners.) Once Microsoft has gotten them to move everything into Azure, Microsoft will be able to work with them more directly and provide more services to them that would traditionally be provided by partners.
(In the interest of full disclosure, I should perhaps mention that I once owned a company that was a Microsoft partner. That's been so long ago that it really isn't even relevant to the discussion, though. More recently, I worked for another such "partner" -- in name only.)