Google is preparing to roll out the updates for the Play Store app. That would make it Google Play Store 4.4, and some new changes in the interface are being worked upon.
You must have noticed before that some of the Google Apps, like Play Books, Play Music, Play Games, Gmail, Maps and Youtube have got a slide out drawer on the side, that has got tabs for navigation. So this time in the update, the Play Store app is likely to get the same type of interface.
Android Police guys got their hands on the screecshots of the still under development 4.4 update for Play Store. Options like the My Apps, My Wishlist which were previously below the action menu are now placed in the drawer and action menu, now only has Settings and Help options. According to Android Police Google will probably be doing a complete revamp of the interface and design and here in screenshots what we see is just a in-progress model.
You can have a look at some more screenshots via the link below.