Let me state outright that cohesion between desperate development environments is overhyped. I fail to see how .NET can promote multilanguage development as an asset, since a fragmented development environment is anything but desirable. For example, if you're developing an application with two people in two languages, what happens if one person leaves? That's a simplified scenario of a major problem.
My previous employer is in the works to move to a new development platform (Oracle Forms) as a means to get applications out the door quicker. They believe that the "Oracle Platform" can produce applications with less time than "conventional" programming. That's all fine and dandy, except for their intent to still use Java for applications. There is one fundamental flaw with this argument that has somehow escaped their view: the addition of another platform only fragments development further instead of unifying it.
This is why I see the Java platform as the only choice for buisness application development. It runs the guantlet for the most diverse set of API's and tools to cover any business need. From web applications and serverside services, to client side applications, Java is the only platform that allows developers to not only diversify to tackle any business need, but all so stay unified on one platform of development. Arguments against Java in the business world commonly point to the lack of Rapid Application Development (RAD) tools. More often then not, they are refering to developing Swing clients without a visual editor. RAD platforms like Visual Basic have their place, but definately not in the business world. Prototyping application with VB is fine, but essentially you've invested time in "throw away code". When it comes down to mission critical, scalable applications, Java has shown it's strength.