With so many millions of people using the Google Play Store on a daily basis, something that might seem minor like a change to the Play Store logo becomes a big deal. The shape of the new Google Play Store logo remains a triangle. Sorry to disappoint you, but rare is the mobile logo that goes through wholesale changes so quickly. The goal is to keep some parts of the old logo so that users can still identify which app they are opening. Among the differences are slightly more rounder corners and the four colors used on the Play Store logo are shaded closer to the actual four colors associated with Google. However, the new logo is darker and not as bright as the current one used for the Play Store. It also appears that the borders between the colors have changed to make them more equal in size. The current version of the Play Store logo is dominated by the blue triangle. You can find the new design in GPay and GooglePay (soon to be known as Wallet) when you make certain transactions on the Play Store such as adding credit to your account. In a situation like that, the Play Store is considered the merchant which is why the logo appears. Google may or may not make an announcement when the Play Store logo is officially changed. Most likely you'll just have to use your powers of observation to note when the change has been made. There have been other revisions made to the marketplace; back in May the Movies & TV tab was removed from the Play Store meaning that those who want to use their mobile devices to buy, rent, or watch streaming movies and television shows have to do so through the Google TV app (which can be installed from the Play Store by tapping on this link).
With the earlier removal of Play Music more than two years ago, Google may eventually want the Play Store to be a dedicated marketplace for Android apps and could spin off games into a separate marketplace.