It's not our plan to remove indexed() from the Algorithms package!
In general, I think it's fair to assume that the standard library version of functionality will always be as good or better than the package version. Ideally we'll strike upon a general solution that allows you to pick up the stdlib version when it's available, while continuing to use the package version when it isn't.
We'll play around with techniques like the one we pitched here to find a good fit for these package to stdlib migrations.