[hughes]

1) and 2) are not a problem if the server accepts any value for the title token (which is the case on stack exchange)

3) is not a problem for hyperlinks (url not visible) or for even direct links (not burdensome length), and if you care about a short url an even shorter form is available

4) seems like a feature? the person sending the link will only ever include as much information as they deem necessary anyway. If the recipient wants more info they'll either request it or click the link.

Trust is an interesting point, but if you can equally put literally anything in the client side anchor (eg. meta.stackexchange.com/questions/148454/#definitely-not-a-rick-roll) so I don't see what a viable alternative would be.