Microsoft informs in Newsletter #2 that they are looking for people who are willing to evaluate an "early access trial" version of their Visual Studio IDE for R, called RTVS (for R Tools for Visual Studio).
Based on the video, RTVS has the same four-window design as RStudio, so there's not an immediate struggle with an unfamiliar layout. David Smith's blog lists some of RTVS's current shortcomings, such as automated package support, that may or may not be a problem for you. I looked for signs that VS might facilitate the integration of R with other languages – such as C# for a front-end and R for the back-end – but not a whiff.
The greatest advantage of RTVS I can see is for IT shops that are comfortable
installing Microsoft products on company PC's but are not comfortable with non-MS, open-source programs like R or RStudio.
The greatest disadvantage of signing up for RTVS is the potential time dealing with bugs that first adopters can expect to uncover.
Comments from willing RTVS first adopters are welcome below.