There really aren't many holes for new calibers. I reckon maybe a .21 or a .23 but that's about it. We have .17s, .19s, .20s, .22s, .24s, .25s, .26s, .27s, .28s, .30s and on up the line. I reckon that did leave room for an .18 and a .29 didn't it? Nope I see no need for a new caliber and likely wouldn't buy one if it were thought up.
GB