Instead of giving new accounts free SP it should be possible to allocate some of your SP to any account temporarily and revoke this SP allocation if malicious behavior is discovered in the future.

So what you're saying is you want the proposed version of voting guilds? :P

Abuse of the Steemit.com registration is a potential issue that should receive more white-hat attacking to mitigate any exploits. So far the owner of those accounts hasn't used them in a very negative fashion as far as I can tell, but it would be more of a problem if he or someone else with a bunch of exploit-acquired accounts does.

As a witness, I have my account creation "fee" set at 20 STEEM. I would lower it to 10 if the goal of "your account is worth $x" is abandoned. Steemit actually makes accounts with their @steem account with their own amount setting actually, but the minimum is the median account creation fee between the witness' settings. Currently, the network median account creation amount is 30 STEEM but the @steem account is making new accounts with 40 Steem Power.

The Steem team are considering alternatives including something similar to your proposal: delegated bandwidth.

The issue with cheaper accounts then becomes namesquatting with the squatter's actual money being used. What happens if it becomes reasonably cheap to namesquat with your own funds? Can you think of a reasonable solution to mitigate that?