Alias dentries that do not correspond to actual physical aliases (ie hard
links) are _very_ nasty to handle.
Creating them is easy (that's what the trivial msdosfs patch does).
Deleting them is non-trivial. Re-naming a file that has aliases is worse.
Right now the dcache has _very_ nice semantics for rename/delete (you can
still follow the dentry tree back to the root, so you get a nice pathname
for the dentry - and one which stays correct even when you rename the
file).
Introducing virtual aliases would break that behaviour (or at least it
would be really horrible to try to support the behaviour correctly).
Linus