Mounts exist. The rear sights would have to go though as they typically use the dovetail.

Not sure how the mass would affect slide movement, reliability, holster/secure, or how you manipulate the slide.

The T1's dot will still disappear or not appear in your field of view much like an mRDS does now. The window size has little to do with it, and the window size on the T1 isn't that much bigger than the mRDS anyways.

The FNP-45 is a pretty well thought out design. Perhaps more practice is needed? I find that if you don't pick the dot up right away, your muzzle is usually pointed too high. With enough practice it comes up quick.

Also, as the FNP-45 cowitnesses the irons to the mRDS, if you can get an iron sight alignment, the dot should be right there. The two sights should compliment each other, rather than replace one another in their function. In other words, use your irons as a crude vector to getting the mRDS dot in view. The mRDS dot once in view, is going to give you the advantage of speed on moving targets, as well as precision at distance.

On the other hand, you may find out that the mRDS is simply not for you. mRDS don't necessarily make handguns better. You may want to stick to the gun's otherwise EXCELLENT iron sights, and put the mRDS on something else.

Hope this helps!