My thoughts on this are pretty straight-forward, and it looks like you've got some of the same ideas in the ticket.

My suggestion would be to look for the use of several different line-endings in the same file and if found, display a dialog informing the user of the counts of each type of line ending with a radio-button next to each type. The default selection for this dialog could be several different things, depending on how you look at it. Anyhow... offer to change all endings to the selected ending, or ignore the discrepancy.

Of course, this feature should be able to be switched off in Padre's preferences.

Regarding the default selection in the dialog, I personally would have a "default line-ending for new files" setting in Padre's preferences with the usual options, and the default of the dialog would be whatever this was set to.

Something that could be nice for newbies could be to somehow annotate, both in Padre's prefs and in the "mixed line-endings" dialog, what the "native" line-ending is for their platform.

Something else I'd probably add is perhaps a little help-button to explain to the novice *why* having mixed line-endings is a bad idea and why it should be fixed, along with what could go wrong (yep, I've seen programmers mix them *on purpose*, with the code depending on it, the bastards ...)

So, that's my $.02... I'm no design guru but I play one on TV.