I think that enterprise market share in the United States will grow significantly with Windows 10. Consumer market share is a more difficult proposition. Ultimately, Microsoft needs to show average consumers what the current incarnation of Windows Phone offers over competing platforms.
They're trying to do this. Most recent ads in the U.S. have been humorous "battles" between Siri and Cortana. I agree that Cortana is more useful than Siri, but this is a feature that is not available on many Windows Phones without going the DP route (which the average consumer simply won't do). On Verizon, the only phone with official Cortana is the M8, so Microsoft is pushing a feature not available on the majority of phones on the largest carrier in the U.S..
To really push WP in the consumer market, Microsoft needs to have a series of ads that address differentiating features all Windows Phone have, and this relates to the design of the UI. It's tremendously useful and smart that that menu items and controls are at the bottom of the screen. This makes them reachable on WP in ways that iOS and Android need to work around. Design an ad with a catchy tune and the theme of "Big Phone, No Strain" and show how all menu items are within easy reach on all phone sizes.
Another UI feature that could be easily highlighted is pinning individual contacts, documents, albums in ways that are can't happen on iOS (though Android can do some similar things). Make an ad with some younger person listening to a catchy tune and pining his/her favorite contacts, musical artists, and OneNote to do lists (mix of social and school/business engagements), and end with the tagline "This is me. This is the new Windows.
Of course, these suggestions have probably been considered and dismissed by the WP marketing teams. I just think that a back-to-basics focus on UI needs to accompany the forward-looking Cortana spots. At the very least, it would give carrier representatives talking points for all of the phones they offer.