[6bone] network's architecture under IPv6

[BEGIN, Thomas]

Hello to all,
I am wondering on IPv6 impacts over a company network's architecture.
I mean, a big IPv4 network has to be divided in several VLANs in order to lighten the available bandwidth (sometimes for security reasons but it is not my interest in this case). And this because broadcast messages are received and examined by all network adapter. 
Thus comes my question: As there is no more broadcast messages but only multicast messages in IPv6, is there still a need to divide a big network in smaller networks (VLANs) ?

Thanks

Thomas BEGIN