Suggestion - Search in the Portable App Directory

This is already planned:

Platform 'Next' Pre-Release Bug Reports
Upcoming Features Confirmed Coming In An Upcoming Pre-Release
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Ability to search app directory
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Well, apparently the enhancement is planned, but I have a feeling that it won't easily be implemented while the Updater/Directory is written in NSIS, meaning that it probably won't be implemented particularly soon.
(There are plans to integrate the updater directly into the Platform in which case it will be written in Delphi [Pascal] which will probably make this feature a little easier to write.)
However, there is another option that can be used in the mean-time: Listary.
Listary allows for find-as-you-type searching of most (if not quite all) lists in Windows, including the PortableApps.com Updater™ / Portable App Directory™, so while the interface is a little bit different from how you described in your request, you might find it to suffice, at least till the desired feature is implemented, and it's even available as a Portable App.
(You might even like the way it works … and the fact that it works just about everywhere.)

P.S. @Gord Caswell: Your link to the Platform 'Next' Pre-Release Bug Reports page is missing a slash.