Q:

Help users create dummy links that are not to unrelated commercial sites

A search for domains like mysite.com provides thousands of results on Stack Overflow and hundreds on Drupal Answers. I sampled some. Each and every one I checked was a post by someone ignorant about http://example.com, http://example.org and .example TLD, as defined in RFC 2606. Other "natural examples" domains are abused pretty much too.
My request is - disallow these:

mysite.TLD
site.TLD
abc.TLD
xyz.TLD
[one letter repeated].TLD

When they are detected, propose http://example.com or http://example.org. With old questions, use robot or find other way to edit them.

Even if SEO is not a problem, professional sites about Internet and associated technologies should not ignore RFC on such a large scale. Not to mention linking porn like about thousand links to xxx.com - I was already detected as one who visits "sites related to content forbidden here" by a firewall or two thanks to that.
I can assure you: you don't want to explain to your boss why are you searching for "adult content" in working hours, or agrotourism farm owner why that happens under his roof. Even WSODs are not nice. Now I think I have SE whitelisted, but anyway... Sadly, firewall was right, I did have xxx.com mentioned in my search results here and on Drupal Answers.

A:

The "adult content" rationale is pretty compelling here. I've blacklisted the following URLs:

http://mysite.com
http://site.com
http://abc.com
http://xyz.com
http://xxx.com
http://foo.com
http://domain.com
http://mydomain.com

...along with variations that include the "www." subdomain, and the .org and .net TLDs.
This doesn't remove existing examples from the site, but will require that they be changed if the post is edited - and will block all new instances from being added. Folks trying to edit any post containing these will now see:

Which links to this page: Why are certain example URLs like http://site.com/ and http://mysite.com/ blocked from post content?
January 9, 2015: this blacklist is now live on all sites EXCEPT for meta.stackexchange.com.

A:

Any links that are actually created accidently like http://mysite.com include a nofollow, so I don't think there are any SEO benefits for those domains anyhow. The only possible problem is someone clicking on said link thinking it goes somewhere useful, but that sounds like an unlikely and insignificant problem to me.
The nofollow is removed if the post is considered reputable enough, so if there truly are a number of "reputable"  posts linking to mysite and whatnot, it may warrant a modification of the nofollow removal logic to skip those links.

