Any user can decide to watch pages or subscribe to RSS feeds from the wiki.
However, there is no way to inform other users that something could be important for them: you have to open your email system and manually create a mail to all the individuals you want to inform and refer to the page URL.
I would be nice to be able to have a quick link on top of a page that would prepare a mail with the link to the page, and that would allow you to pick User Groups and/or individual users from the wiki. The user preparing this alert would be allowed to change the mail content. to add some relevant information.
Once confirmed, the system would send an email to all the users targeted (as individuals or as part of User Groups); the system would be able to send only one email to a user being part of several User Groups targeted by the alert.