In the future men will be able to carry children just like women

[Alex K]

The traditional family model works fairly well.

Parents have a high level of motivation to look after their own contribution to the gene pool, children are benefited psychologically by contact and bonding in general with the parents.  

I don't understand why there shouldn't be any bond with the parents like you're suggesting.

I've never felt any bond with my parents or other of my family after a certain age. Pretending otherwise has been a drag.

That's you then, a personal anecdote. Nothing one necessarily needs to model all of society after. But having said that, I'm all for keeping it flexible, in most cases the usual family model (and I include same sex couples etc. in my picture of "traditional family" where you have two main caregivers acting as parents) works out great, in many, it just doesn't at all, and other arrangements should be made possible.
In a sense, we are taking steps towards such a "decentralized" model already, e.g. our kid also lives in such an extended tribe because she goes to an excellent daycare facility where she has relationships with multiple adults and children who are, for all intents and purposes, acting as her extended family.