Firstly I’d agree with the majority of the comments that state that the proposed change would hurt minnows.
As for the idea of withholding funds earned for a period of time, I think long term it wouldn’t make a difference. The biggest and most successful spammers are carrying out their operations using dozens if not hundreds of different accounts. All they would need do is wait for the said period to end and then they are free to spam again. Seeing as these individuals are creating accounts on such a frequent basis, the whole process of account creation - waiting for restrictions on funds to lift - spamming, would only need to complete once for them to have a steady stream of revenue again.
Most of the ideas on here are very much from the “stick” end of the solution. Where are the “carrots”? How about some onboarding for newbies? An arm around the shoulder to help them get started and know what is acceptable and what’s not? Steemit already produces those badges for certain achievements. Perhaps an enhanced version of those for new users who are playing by the rules? If these were visible on a new users account for a certain period then it would almost act as a verification of them as a genuine community member. I think it’s worth remembering that not all new users spam!