the CLI util as representative of the general class of 'things launchable via curl, i.e. just with get requests to specific addresses'
Ok, well in that case, no - you can't launch a Designer with curl.
You can put designer://localhost:8088 into a browser, which is paying attention to custom URL protocol handlers registered with your system.
But curl doesn't care.
kevin@DV-kevin ~ [127]> curl designer://localhost:8088
curl: (1) Protocol "designer" not supported
Interesting, what does this mean then?
On a linux system you might run something like xdg-open designer://localhost:8088 and it might open a browser to that URL, or use the registered URL handler to try to open a Designer (Launcher?).
It can of you edit the designer launcher's json config 
I recently renamed all of my connections into a standard format: DEV/PROD_CUSTOMER_HOSTNAME_SOMEOTHERSTUFF
and then sorted via python, and it's actually not so bad to use in list mode now
Following up on this for 8.1 or Mac users…
I went down the deep-link rabbit hole but was unsuccessful and opened a support ticket with IA (177260).
If you're on 8.1 deep-linking to a specific project isn't fully implemented yet — it'll open the Designer Launcher but won't actually load the project. IA is aware and said they'll follow up when that changes.
For 8.3 users it does work, and if you're on macOS Tahoe there was a specific deep-link bug fixed in 8.3.5 (IGN-15850): Nightly 8.3 Changelogs - 2026 and beyond - #58 by system
To be clear, 8.1 is never going to get deep linking directly into a project in the designer launcher.