First of all, additional link attributes are disabled by default, not to disrupt existing projects.
To enable them you should add this to your property definition:
However, currently it’s not possible to use both old Aloha format definitions and the new format, the Aloha format would be discarded. But this behavior is now fixed in master, so since the next release (which should happen quite soon), you should be able to mix the old and the new config format again.
But even better than that, there’ll be an automated migration from the old format to the new one: https://github.com/neos/neos-ui/pull/2120
Anyways, sorry for the confusion, hope this post cleared it up a bit.