Well, the nunchuk for the Wii has two triggers, as do most other controllers these days on each side of said controllers. Having two triggers on both parts of your controller would be a start. Replicating the functionality of both the Wiimote/Nunchuk and a DualShock seems to be a big factor for you, so, yeah.
Also, I'm not a fan of the Wii's IR sensor method. It doesn't give me the flexibility I'd want in many cases, and that's something that Wii MotionPlus doesn't alleviate. I blame the sensor bar's size (which is just two IR LEDs anyway), the visual range of the Wiimote's IR sensor, and the lack of decent calibration options. It may be better than the Power Glove's three sensors, but to be honest, I like the way Sony's going with their own motion wand with having the PS3 Eye (or in this case, just some sort of camera) detect the controller, rather than the other way around. Sure, that big glowing lightbulb on each controller looks weird, but at least it provides detection of the controller from more angles, both of the player relative to the TV/camera, and of the controller itself.
But for sake of argument, let's say you're going to stick with the IR sensor method. This will sound redundant with my last paragraph, but add a calibration option to the system, let me place the two IR LEDs (maybe three-LED arrays so the controller can detect which corner it's looking at) on the edges of the TV (maybe even four so I can place them on the bottom two corners as well), and increase the capture range of the IR sensor. Also, I would suggest putting the IR sensor on both parts of the controller. Using a bow and arrow with the Wiimote and Nunchuk is largely unsatisfying because the nunchuk has no idea where it is in relation.