How URL Shorteners Should Change

When I view ~10 year old web sites and forums it's rare enough that external links work at all, with all these link shorteners it's going to be even worse.

I imagine in the not too distant future that link shorteners will no longer be used (for one of many reasons), if/when that day comes most link shortening sites will have no incentive to keep their service available, and it would be hugely tempting for them to modify existing links to display relevant targeted ads, instead of the destination pages. Hell I wouldn't be surprised if many of them exist purely with that intention.

I'm 100% with you here. But it will take time for that to become common. Until then, we can improve the existing situation a bit.

they should simplify them, without single focus on as short as possible

Why? Twitters URL shortener is also used to prevent spamming. In addition Twitter tries to detect malicious content and warn the user about it. They have reasons why they lengthen shortened links...