The following question was raised by Ilya Ryzhenkov, via the BCL web page: "[I] just found myself in [the] situation when I need ICollection with Add, Remove, Contains but no indexed access like insert, this, and IndexOf. Actually, this what probably best suites to name "List". So, are you going to add more collection kinds or not?"
Ilya, we're very focussed on Generic collections right now. With the introduction of generics, we want to make sure we're providing generic solutions which meet the needs of collection consumers, and provide at least an as good, and generally better story than the existing base collections. We will continue to explore the potential for additional collections, but the next release will be primarily focused on generic collections.