Hi Sheila!
The short answer is: Yes - that is the plan, but not imminently.
One of the major themes that Rally is investing in at the moment is trying to modernize our User Interface in terms of its look and feel, usability and the technology that powers it. As you work your way through Rally you can easily point out pages (or features) that are out of date or less streamlined than others. The original Custom List falls into the "out of date" category and presents a lot of serious technical issues in trying to implement the changes necessary to bring it up to date.
However, it remains one of our most useful applications so we absolutely did not want to leave it sit knowing what it could be. This left us with our best option being to create a new Custom List in our modern framework as a replacement.
With regards to timing... a couple things:
1. There are still features that must be implemented before we can even deprecate the original Custom List app. It must support the free form query option that you can access through App Settings and it must allow for selection of all the item types that the original does
2. When we are at a point where we have reached that parity, we intend to communicate that timeline with enough time for folks to migrate, and we will be available to help give guidance and help to anyone that needs it. There is even the possibility for us to investigate a migration tool should it be necessary.
Thank you for the question Sheila, I hope this has been a helpful answer.
-Nate