Our goal, is to deliver a great user experience. For a vast majority of our users the platform/tools are secondary.
We considered supporting a secondary search provider written in .NET, but when we asked ourselves, "who would want to use this other provider" the answer was always no one. Why would you want a version of search that couldn't find results?
You do not have to write any code in Java to use Solr, it is highly extensible with tons of add-ons, and makes search orders of magnitude better. (Did you notice you can search for people, groups, etc?).
Search is an integral part of Evolution. We could not afford to compromise, even if that meant requiring a some additional installation steps (NOTE: IMO, the new search is far easier to setup and maintain than the previous Enterprise Search).
Thanks,
Scott