More control over IPs used in IIS for site hosting.
Sites in Plesk can have only one IP address assigned; this IP must the the same for FTP, HTTP, etc. A change to allow more flexibility should be easy to implement (e.g., allow 'all unassigned'), so sites running on Plesk can be used in load balanced scenario's, e.g. when running Plesk on a cloud server.
Numa Schmeder commented
Have the option to have multiple IP per subscriptions, this is very important, mostly for ssl websites and load balancing.