We currently use Do-more PLCs and are considering BRX as well.
On both platforms, it would be nice to have separate high speed input and high speed output cards. For our applications, we typically use a lot of high speed inputs but very few high speed outputs (encoders mostly but also an application where we are monitoring inputs from 30+ photoeyes).
For one particular application, we need 32 high speed inputs and no high speed outputs. With the BRX, that means buying 4 cards and having 32 unused outputs (I'm not counting the built in high speed io you can get on the base unit). It sure would be nice to get by with 2 16-point high speed input cards.