I can think of one reason. The price tag. More features equals more money to add in the new features. Still, dreaming sometimes leads to improvement. I'm sure others will probably weigh in on this.
Talon
It is a fact of life, more features higher price, but much better Pleos, cannot keep the price the same without adding more features. I would rather pay more and get a better Pleo. I will love to see what they do next.
Also more movements, and random at that, so each day is not the same, or does not do the same moves each time, kind of boring. Face recognition, in the way Xbox 360 uses Kinect and the new Samsung Smart tv's, so you wave to get Pleo attention to preform tricks.
Also a way where Pleo has to learn the tricks, like a real dog, a praise and treats as a reward for doing tricks, rather then the stones now, as he is not really learning tricks. So much more life like if pleo has to learn them like a real dog. Kintec and sight would be a good way to interact with Pleo, he sees you, and sits there, you say his name and reacts. And hand gestures he does tricks, but feel like a real dog, he has to learn tricks, and learns by doing certian things he gets a reward.
I am not a fan of the stone idea, as he needs to actually learn tricks. Also an option where you can seen on a screen what Pleo is seeing with his camera, so needs to be wifi capable.
Pleo more lifelike, while the laughing and other animal noises are kind of funny, makes Pleo more like a toy rather than imitating as best they can a baby dinosaur, am sure a baby dinosaur would not make these sounds, so a much more life like Pleo Please. So Pleo needs a much more serious nature, or at least the option to turn these non life like sounds off. I mean the laughing is something animals do not do, so needs an option where he can be hooked up to computer with a menu of options to turn things on and off and customize him the way you want, so if you want these funny no real sounds then fine, if not the option to turn them off, or replace sounds, so downloadable sounds would be great.
For Pleo to hook up to PC, it needs to be simple menus so even the average person can use. Skin you can replace yourself, which could lead to you being able to buy costume skins and replace the skin yourself when it gets to warn.
As has been said a self charging station, so when he gets low on power finds it and charges himself. Sensors not only in the front for object detection, but behind and on the sides also, so has object and avoidance detection all around in all directions, so less likely to get into trouble and get stuck, etc.