I'd also like to see some of the canine toys with fully engorged knots having a smaller stem behind the knot, more like real life. This would allow you to really lock in and I think it would feel fantastic!
The only problem I see with this is "stability" for those that want to ride the toy, because I have one like this. Having a narrower shaft behind the knot makes it harder to stand up on its own, and with enough pressure, would just wiggle around and/or try to slip out from underneath you.
The only way I can think to possibly fix this would be to add a short, but thick enough core into the base of the toy that just barely goes up into the knot. It may not let it stand up on its own, but it would prevent the second issue I mentioned.