I have heard the MTH electro couplers are pretty bad unfortunately, they don't work well. On the subject of couplers, I would like to see couplers in HO that actually stay coupled with ease, like the lionel O gauge ones, only more scale in size. The one thing I dislike about smaller scales is the constant uncoupling.
More importantly though, I would like to see Atlas release some PRR or B&O like position signals that are easy to hook up. I think their plug n' play modern color signals are amazing and it would be nice to see them expand the product line. Or how about some hefty signal bridges?
More crossing flashers, ones that actually operate and are easy to wire up. MTH has the right idea with this, I have no idea when they will be released.
Lastly, it would be great to see more observation cars with lit drumheads and marker lights. Why is it that Kato has released such great Broadway Limited cars in N scale, but there is has never been a PRR set like this in HO?
BLI made some great zephyr cars, but thats about it in HO so far.
Other than that, I'm pretty happy with the way things in the hobby are going, there is a lot more stuff out today that one couldn't even dream of 10-15 years ago, so I guess I shouldn't complain at all. Walthers, BLI, MTH, Spectrum, all great stuff for HO.