T-Mobile to Sunset MetroPCS's CDMA Network by 2015

I doubt there will be much alienation of the customer base. Your average customer doesn't care if they're using VoLTE, CDMA, GSM, HSPA, or magic... if the call goes through, its clear, and they can get service where ever they want to use their phone, that's the extent of what the average person cares about their voice calls.

Only people interested in the intricate technical aspects care about it being VoLTE, and frankly those people are about as far from MetroPCS's target customer as you can get.

Like you said, VoLTE is bringing Metro's LTE network to its knees because of the lack of spectrum. For 99.999% of Metro's customers; getting a new phone, having a larger native network with full speed data access, having their data speeds increase dramatically, and have a much larger roaming network; will be considered a huge improvement. Not only would that 99.999% not care one bit that they are no longer using VoLTE for their voice calls, for them the change over couldn't come fastest enough. Those customers will be pushing Metro to make changes much faster than 2015.