You can add your own hotlink behaviour for &chans.
ON *:HOTLINK:&*:*:if ($hotlink(event) == dclick) join $hotlink(word)
Only Khaled can confirm, but I'm pretty sure the linking of &channels was removed because of confusion with user and channel modes, and the fact that &channels tend to represent an extremely small (and ever decreasing) portion of network channels. Messaging somebody a &channel link typically doesn't even make sense on many networks, as there is a good chance the users won't end up in the same channel (due to the server-specific behaviour of &channels), so I can't even imagine how often &channels are shared in public, let alone used in private. Fortunately if you do need it, it's pretty easy to add back via the above script.