I assume that there is no way to have a custom hostname, or any other portion of the URL be in any way meaningful to a person glancing at their browser's location bar (where available; sorry mac users), but is that right?
The environment unique ID, at least, can be customized and this gives the app maker a little freedom to tell a user where they are, at least. Everything else is pretty much arbitrary, meaningless to your business and your developers, alike.
I can see that there is a short URL suffix allowed, which is a less convenient version of a bookmark for probably at most one developers' satisfaction or mild amusement, taking us directly back to one of these:
https://<environment unique id>.<crm9 or whatever>.dynamics.com/main.aspx?appid=<UUIDUUID-UUID-UUID-UUIDUUIDUUID>&gibberish=<more UUIDS>&what_now=<UUID>
The short URL offers a chance for tenths-of-a-second long appearances in the browser's URL bar, like one of these:
https://<environment unique id>.<crm9 or whatever>.dynamics.com/apps/<up to 20 characters>
... at which point, trying to bookmark it will just bookmark the inscrutable version that is indistinguishable from any other apps on the same environment (and different environments, by default, unless you memorize hexadecimal numbers following "org").
Is there any way to extend that as a basis for a moderately succinct deep link? I don't think so. I'm not sure how it came to pass that something straightforward like the below was never made possible:
https://<environment unique id>.<crm9 or whatever>.dynamics.com/apps/<up to 20 characters>?<custom parameter>=<useful value>
A lot of other platforms would give you a mechanism to at least carry forward some parameters through the redirect, possibly even a POST, but they're discarded first, in model driven apps.
Hopefully I'm just all wrong about this? If there's a document explaining additional capabilities, I just haven't been able to find it, and it doesn't seem like something power apps developers talk about. I think most of us have used internet web sites before, and are used to at least gleaning some bare minimum of information from links.
I'm also a little curious if anyone may have written an entire proxy, to hide all of this from a set of users? I'm thinking of something that would allow for branded, quasi-meaningful URLs to be methodically transformed into the more inscrutable, ungainly requests endemic to power apps. It doesn't seem like a very "Power apps" thing to do, but potentially, if your system has the kind of value so many apps in internet history have had, there could be someone for whom it is worth that extra layer of effort.