In reply to Justin Tadlock.

I'd argue that the experience of browsing through that many themes isn't much better in the admin. The in-Customizer version is exactly the same UI, just in one column. Search, etc. can help but ultimately you're going to have to visually browse through all of them or search for a specific theme either way. We need a fundamentally different approach for both places to make it easier to handle having that many themes on a site.

For everyone with scaling-type issues, probably worth noting that we're planning on bumping out the Customizer controls area to almost full-width when we add theme-install, which is more the process where the entire focus is on finding a theme out of a large collection, whereas browsing installed themes is more limited (except in multisite-type setups).