Due to the limitation of https://big.ideas.aha.io/ideas/APP-I-2665 , we compromised to put all the products in one ideas portal. Currently we have about 10+ products in this list and it could easily grow into tripple digits. With that many products under one ideas portal, the SSO configuratoin, Branding etc beomes senstive to open 40+ product owners... anyone could accidentally change something would be risky and things can get escalated.. resulting in lots of noise.
So, it would be helpful to impose the privilege on the ideas portal that the creator or the admin should have the editable privilege and others could have the read-only privilege.
We recently launched three new administrator roles to allow for greater flexibility around managing and configuring accounts. Under this new structure, now only those with Customizations Admin privileges have the ability to configure Ideas portals. You can read more about it here: http://blog.aha.io/admin-user-permissions/
While we understand that this doesn't completely solve your use case in providing read-only access, it may help to potentially limit editing access.
At this time, we do not have plans for additional updates in this specific area but hope that the workaround can help. We hope you can understand.