the only complication that i can think of is that unlike private keys (HD wallets) in a password manager you have no way of knowing how many passwords you have used because there is no "public key" and "blockchain" to check which one was used. which can be solved if you keep a backup on the cloud only from the "paths" like this:
bitcointalk.org -> path=m/1/3
google.com -> path=m/2/5
...
the first number can be the "account" for different websites and the second number is the number of passwords you have already used like when changing the password every now and then you create the next one.
of course there is the additional risk of not being careful and creating the same thing twice.
This would make it necessary to keep the backup up-to-date with the latest 'version' of your HD password manager file.
Which.. destroys the purpose one want to use a HD password manager (to not having to update all backups after changing / updating a password).
Different password policies for each site
easily solvable by treating the derived bytes as the fixed entropy used to derive a password from. or simply use a certain encoding that only gives you the allowed characters! for example if it doesn't allow symbols then use base-62 (10 num + 2*26 letter (lower+upper)!
Password revocation
then you derive the next one. m/1/3+1=m/1/4
Again, both of these approaches need you to update your backup file regularly after changes.
If you need to do this, you don't have a reason to use a HD password manager.
The whole sense of a HD password manager is to have 1 backup file generated, and not having to update it anymore.
Without this advantage, there is no good reason to use a HD manager instead of a standard password manager.
You can't store already existing passwords / private keys / etc.[/li][/list]
the whole point is not storing them but creating them on the fly.
But you still can't add other sensitive information which you want to be stored inside there.
If i want to store my private key to a specific address there.. i can't. Obviously i do not want to create a new one in this scenario.. i want to save a specific one saved there.
This works in standard password managers, but not in a HD one.
In the end, if you need to update the backup file, you only have disadvantages - and no advantages - using a HD password manager compared to a 'normal' one.