You could bind it to a Compose key sequence, e.g. "Compose+Space Space". (Analogous to em-dash, which is "Compose-Hyphen Hyphen".) But it's still an extra key

You could bind it to a Compose key sequence, e.g. "Compose+Space Space". (Analogous to em-dash, which is "Compose-Hyphen Hyphen".) But it's still an extra keystroke. And I worry that I'd cause problems editing non-UTF-8 documents if I retrained my fingers to use it at the end of every sentence and then didn't remember to switch back to the ASCII way of doing things.