one of Our iPad mini’s has been plugged in for several years now. No issues so far. It’s just now mounted more neatly to the wall now. I have heard about the possibility of the battery bulging, but haven’t had any issues myself. My brother in-law has 3 that have been plugged in longer than mine have been. Not saying it can’t happen, but the chances are slim from the reading I’ve done.
I haven’t made any for larger iPads, but the process is the same.