I'd say the admin app already looks a bit like Bootstrap, and it's hard to claim either in its default form is more or less "homely" than the other. Granted, I like both.
Also, the admin app isn't supposed to be client-facing; it's a very effective but not-extremely-user-friendly way to view data without having to resort to SSH'ing in and running ORM queries on Django's CLI (or, worse, the database's CLI).
You can use it that way (and many of us have; I'm not innocent), but encouraging that with a pretty application of Bootstrap will likely give a lot of new developers the wrong idea on the tool's purpose.
I think keeping it ugly does Django a disservice. People associate the hideous yellow on cyan header with it and might think ... oh that rails/node stuff looks more professional (less like it was created by 90's-IT-guy). No matter that the issues are orthogonal, people aren't aware of the nuances.
The widgets are fine-looking, though increasingly dated. Why not outsource this work to someone who cares about it? Its community must dwarf Django's.
There's some truth to your statement about encouragement, but it reminds me of the phrase, don't "cut off your nose to spite your face." Plus, it isn't the author's place to dictate how the user will use it.
Also, the admin app isn't supposed to be client-facing; it's a very effective but not-extremely-user-friendly way to view data without having to resort to SSH'ing in and running ORM queries on Django's CLI (or, worse, the database's CLI).
You can use it that way (and many of us have; I'm not innocent), but encouraging that with a pretty application of Bootstrap will likely give a lot of new developers the wrong idea on the tool's purpose.