Update field based on people in a preference list

Hi everyone, 

We have started using the new preference lists but since we have different brands we have different preference centers / forms. 

One of our biggest struggles with preference lists is that you can't add people automatically to them from a sign up form, which means that we always need to work with two "include" lists when we send newsletters. Our general lists are based on dynamic distribution lists that look at a certain field. To give an example. 

When people sign up for one of our newsletter we have a hidden field that is called "Newsletter" with the value "Sharing". We have then a dynamic distribution list that is based on a report in Sell that includes everyone that has the value "Sharing" in the field "Newsletter". 

At the same time we have a preference list "Sharing" that people can subscribe and unsubscribe" from. Ideally we would like to be able that everyone that "subscribes" for the Sharing list is added to our distribution list and gets the value "Sharing" in the newsletter field. 

My idea to solve this is by creating a nurture that has the only workflow to update the newsletter field with the value "Sharing". I would then have the preference list "Sharing" with opt-in as include and set the auto refresh to "daily". The nuture would also get the option that people can enter it multiple times. In that case the nurture should look once a day if somebody is new in the preference list "Sharing" and add these people to the nurture and update the field. Then our dynamic distribution list is updated with these contacts, and it should be possible to only use one list when sending emails. 

Anyone who tested this or can confirm my thoughts?