Despite being tremendously useful for some folks, Google Wallet isn't always given much attention. It seems Google wants to do more to get you using Wallet, placing it within Gmail, arguably one of their premier products.
It seems that the change will bring a $ button to the email compose window. Lurking behind this button will be a popup button, allowing the input of funds for immediate transfer to the email recipient's Wallet. This is probably the smallest bit of Google news you'll have seen today, but it should prove a nice addition.
The Wallet functionality within Google already allows you to buy things from the Play Store, and it never was particularly difficult to sent cash through it in the first place, but now it'll take a fairly large position within the Gmail compose window.
We don't have any ETA for when it'll be available to everyone, but it doesn't seem likely that you'll get it overnight. It didn't stop me from checking anyway. Google also has provided a video of how the functionality works, though it's more or less self-explanatory.
Source: Google Youtube video