dashbord/horizon create network for vlan without choosing segmentation ID

I think you are talking about the provider network feature in Neutron.

At now network creation form does not support provider network feature in Neutron. The blueprint is proposed to allow admin to specify the segmentation ID, but I don't see any progress.

The segmentation ID depends on the network type of the network, so it is not simple to validate user input. If we can pass the parameters to Neutron without any cross-field validation, it can be implemented. However, it is not user-friendly.

I would like to know your thought on in for better implementation.
If it is small, we can consider a fix in Havana-RC1.

I think you are right, this is much more complicated then I expected. Though, not less important. I tried to search for a blueprint to add the existing networking CLI commands to the Horizon but didn't find any.
I think that the simplest implementation will be the best, both for the programmer and the user. Means, while creating a new network assuming the creator knows which of the network types he want, a new network panel will open (vlan, local, gre), i.e. 3 different new network panels instead of the existing one now. This might affect other panel as well.
I can't measure the change and it's effects because I don't know the data structure of the system.
For now, you can just add the opurtunity of adding some new features to a network, such as ID, for the user to choose if using them or not.

I think blueprint quantum-network-provider-types will fix this problem since it will add the ability for an admin to choose provider network settings when creating a network.

Fix proposed to branch: master
Review: https://review.openstack.org/74066

Reviewed: https://review.openstack.org/74066
Committed: https://git.openstack.org/cgit/openstack/horizon/commit/?id=b4fb18198c0ecf9db02e3b5873fa66d58fb4e1d2
Submitter: Jenkins
Branch: master

commit b4fb18198c0ecf9db02e3b5873fa66d58fb4e1d2
Author: Justin Pomeroy <email address hidden>
Date: Mon Feb 17 08:49:42 2014 -0600

    Support provider network extension when creating network

    This adds the ability for admins to set the provider network
    settings when creating a network. This includes the network type,
    physical network, and segmentation ID. These options will only be
    available if the provider network neutron extension is supported.

    Change-Id: I6108504a92a32f067cf151ec103171a7bbb601df
    Implements: blueprint quantum-network-provider-types
    Closes-Bug: 1223360