It would be interesting, as it would prove Google fans wrong, most of whom insist that the ONLY reason Google isn't bringing their apps to WP/WM is its poor market share. As it currently stands, WP/WM now has even less market share than when that argument's popularity was at its height.
Anyway, I have no idea. I'm sceptical. I'll have to see it to believe it. MS having conceded the smartphone app market (Astoria and Islandwood) to its competitors would certainly make it easier for Google to get on board. If I were Google, and MS promised me that Astoria and Islandwood would be made available for free to anyone who wants it, I'd get on board. If I were Microsoft, I wouldn't do that.
Will be interesting to watch...
Either way, I don't think Waze would count as one of Google's core apps. I'm thinking more Gmail, Calendar, YouTube and Maps.