The ability to equate sub domains (and not just domains) would be a useful feature.
LastPass's current implementation of equivalent domains only allows the user to equate top level domains, not sub-domains. For example, you can equate example.net and example.com, but not a.example.com with b.example.net.
In my case, the reason this feature would be useful is because I have various accounts (which are not linked to a single authentication database) at work in which I've had to configure "exact host matching" URL rules within LastPass for my employers internal domain; however, there are a few sites which are equivalent, and it would be fantastic if I could equate those sub-domains. In the meantime, I've had to create two separate LastPass sites to accommodate this setup.