My sis is pg. She and her bf are pretty conventional and are only really thinking carrier/sling because they live on a boat and a pram would be a nuisance.
I feel that a ring sling would be a good start for a little bub, but i never used my sling for long walks - just around the house and little outings. I used my HaB for longer periods of carrying. I did have 4 idifferent ones in the end.

I am well out of the loop and i have seen some amazing wraps and things, but i don't want to buy her one that can only be used for one thing and then find she needs another one too.

I was thinking an ergo? More conventional, a bit structured but not like a baby bjorn. Can back carry for later?

I really don't know. Would appreciate some ideas.