Good points, Koby.
With regard to the future direction of GV and the consumer land-line telephony marketplace, I've frequently written about this on the Google Voice forum. I get a lot of flack from the
soreheads and whiners valued community members who don't have the business or legal background to understand the larger issues, and just want free phone service. Here's a recap:
Google, of course, hasn't and won't announce future plans; they're infamous for their silence. But, all indications are that the inbound call management and other original features of GV from the Grandcentral days will remain pretty much intact (they'll give you one phone number that, in turn, forwards to up to six of your phone numbers, etc.) The "free through the end of 201x" limited offer language was eliminated in 2013 when Hangouts phone calling was introduced. Now, future pricing can be understood as any business product or service: "It's free as long as we continue to offer it for free, and we reserve the right to change our pricing, or the offer itself, at any time." I do not see Google having any interest in being in the telephone services-for-a-fee business, as they really want to stay away from FCC regulations and the mandatory fees, surcharges and taxes that come with regulation.
Your point about users turning to mobile vs. VoIP is right on. Google is moving in the same direction. The "pure play" or independent VoIP marketplace is already saturated, with race-to-the bottom pricing and extremely low profit margins. It is a relatively small niche market at this point for consumers (although more robust for business users), for several reasons. Most residential consumers are either getting phone service as part of a 2-way or 3-way bundle with TV and/or internet service now, or they are abandoning it in favor of mobile phone use. There is no sensible business reason for Google to be in the land line VoIP telephone service provider marketplace.
As to whether or not Google's exit from XMPP support will have any effect on the pure play consumer/residential/SOHO VoIP marketplace, one could argue either way. A year from now, everybody will have forgotten about it; there will continue to be the come-and-go small providers, but the more stable providers will probably still be priced around where they were before and during GV times.
This year, we expect to see increasing migration and integration of Google Voice functions over to Hangouts, where users will continue to be able to make telephone calls (free to the US and Canada, low-rates elsewhere) on their laptop or desktop computer, on their iOS device, and soon, on their Android devices.