Not sure what you mean by 'attached keypad', I have the clip on 'message pad' for the DS4 but you can only use that wherever text input is required. It can't be used to map control bindings to.
I got one of these types of clip-on chatpads: clicky but it's even not very good for inputting text, as it's missing / annoying to enter some things like systems iirc.
At one point I thought it would be great to use it for actual game commands though: as it's right by your thumbs and could quick access to things not normally bound, like quick heat sink deployment. Now I don't really miss the keyboard, as even on PC I use a HOTAS or DS4, but I still would support the option to have keyboard control available.
It may also help smooth concerns if cross-play ever happens.
Again I think the fact PC already has KB+M vs HOTAS vs controller players, console users would be at little more a disadvantage than a PC player using a controller.