As others have mentioned throughout this thread, PowerShell isn't going anywhere. We're investing considerably in the PowerShell ecosystem. PowerShell/WMF 5.0 just came out with a ton of new features[1], and we're not slowing down any time soon.
Because it's operating mostly in user mode today, Bash on Windows is much more suited to developer scenarios. I've already played with workflows where I'm running vim inside of Bash on Windows to edit PowerShell scripts that I'm executing in a separate PowerShell prompt. In fact, I can plug along fine in a PowerShell window, run a quick 'bash -c 'vim /mnt/c/foo.ps1'', make a few edits, and be right back inside my existing PS prompt. This really is just another (really freaking awesome) tool in your toolbox.
[1] http://msdn.microsoft.com/en-us/powershell/wmf/releaseNotes