They do not currently have a Channel for Constant Contact… So, not at this point for Constant Contact at least. If Constant Contact has public API's, you may be able to access those through the Quick Base Webhook channel. Unfortunately, unless Constant Contact has the ability to send their own webhooks, I am not sure if you will be able to trigger on Constant Contact events. They have a functionality that allows you to "Link a Record", but I have not played with that to see if it works through generic webhooks or if it only works with current active Channels. I am a bit surprised that Constant Contact is not a channel they have and was not in the planning stages, at least before they removed all the Upcoming Channels for us to view and now just show this... "Disclaimer: We are working to launch these channels, but plans may change and we cannot guarantee specific delivery dates or that we'll ever deliver certain channels at all."
You can "unsubscribe" a user based on a trigger from quick base in mailchimp. So yes I would think it is easily doable if using mailchimp. There is no connection to constant contact right now.
I also need to update it at some time to let categories carry through if possible. Right now it is one master list. But it would be great to subdivide