The first is already possible, albeit not quite in the manner you may be speaking.
The second, there's already a built-in option for limiting the posting of links. For the method you describe, I believe there are options in the Marketplace to accomplish that.
The third, would need to be an add-on at this point. Don't know if it'll make it into a future version of the software, as that's up to the developers to decide.
I believe Jay's point was that the more work someone has to do or go through just to join a community, the less likely they are to join.
Why join one community that all but requires a DNA sample, finger print and retina scan to join when another community doesn't require it? There's a point where the security measures become a problem instead of a help.
As the spammers make use of software that's been designed to get around those new measures, the new members who would have joined your community are deciding it's not worth the hassle. So the trick isn't to always implement more and more ways to stop spammers, but sometimes to improve the current ways to become more effective. Not only cause problems for the spammers, but not put a noticeable burden on the real people who would join.
Here's an example of an idea that seems brilliant in theory but that I personally believe is more of a pest. Those security codes printed on the back of credit cards. That's somehow supposed to stop/cripple or slow down those that steal credit card numbers, because when making a purchase, if that code isn't used as well, the transaction gets stopped. The problem with that is that all the thieves have to do is include that number when stealing the information. Supposedly, if someone copies the card, then it won't have the security code on the back, making it useless. Um, hello, if someone is making a copy of an actual card, what's to stop them from just writing down the number from the back of the card? I'm sure it's helped to cut down on theft some, but now as a price for that little gain, everyone must spend an extra few seconds on many transactions to enter in the number.
So while the idea of adding in more and more steps to prevent spamming may sound brilliant up front, deeper down it may be nothing more than a nuisance that stops real people from joining, while the spammers still get through. They either get through because of developed software or because the spammers have no life so it doesn't bother them to register on a site. The real way to cut down on spamming is to find a way to make it more hassle and less profit, while not causing an inconvenience for legitimate visitors. Do that and you'll be famous and possibly rich beyond belief.