My first thought was to expand the WDI package but ended up rewriting everything under the hood to make it more efficient and fault tolerant and it didn't seem to me that the WDI package was still actively maintained. If you use wbstats it should remind you of WDI and that's on purpose. I liked the way you interfaced with WDI so I tried to keep that flavor and also make it easier for people who were using WDI to get started with wbstats.
A couple other features that wbstats has.... 1) is that when querying multiple attributes, they are returned in a long data format as apposed to wide. This makes it much easier to use packages such as dplyr or ggplot2 and 2) is the ability to return dates as POSIXct for easy integration into plotting and time-series analysis techniques. The POSIXct really comes in handy when using monthly or quarterly data, since the default format the the API returns are e.g. "2000M12" or "1999Q3"
hope this helps!