Over at tsurupeta.info, there's an ongoing explanation of the hijitsuzai seishounen reform proposal, or what some have been calling the Loli ban. According to the gentleman behind tsurupeta, they are wrong:
This proposal does not directly ban pornographic manga and anime involving underage characters, or create additional restrictions to the distribution and sale of materials that were already marked as 18+. In particular, this is not a “loli ban” as some have called it. Some provisions related to “staving off the proliferation of sexual visual depictions of youths” are contrived enough that they might conceivably cause difficulties of a political or administrative nature for publishers of lolicon manga, but not legal trouble per se as none of those provisions are legally enforceable. It is true, however, that the people who crafted the proposal are also vocal supporters of a national ban on pornography with fictional minors.
Basically, material deemed 'harmful' under Tokyo law will have to be kept out of sight of minors, but it won't actually be banned, and that's an important distinction that may not be getting enough attention. Still, obviously calling it a 'loli ban' is an over-generalization, but if my understanding is correct, the 'contrivances' mentioned could have a similar effect; the new law would give prefectural authorities the right to take "harmful" materials off of the shelves, if they claimed that minors were in danger of seeing them. Technically nothing is being banned, but I don't know if the fact that publishers are not in "legal trouble per se" is going to be much of a consolation if their stuff is being removed from shelves.
It's stuff like ShoComi that really stands to be hurt by this; keeping this stuff out of the hands of minors may sound reasonable enough, but some of the stuff they want removed has always been targeted at, and intended for, minors. While it may be the first thing to come to mind when this subject is broached, stuff like hardcore lolicon doujinshi isn't sold through official channels, and is more or less beneath the Diet's consideration (at least for now.) However, I freely admit that my concerns come from merely a casual observer of the situation; if you're interested in more specific information on the legality of the situation, definitely take a gander at tsurupeta.info.