They may, but it won't be because of MetroPCS. By the time MetroPCS gets merged in, TMo will have LTE-A across at least part of their footprint.
Their combined footprint is tiny.T-Mobile's right now is tiny.
What's tiny? T-Mobile's coverage? Not really...it's just clustered around big cities. MetroPCS, sure, it's tiny...also clustered around big cities. Just a smaller number of big cities.But T-Mobile's overall coverage isn't tiny, unless you're removing all population centers from the calculation.