I'm a fan of "quarterly" proposals. But I don't see why this must be blockchain enforced. The front-ends can just allow you to filter "unlikely to fund" proposals, depending on the user's preference.
I also wouldn't be upset if there was a blockchain enforced process either.
You're right that the "attention" part could be resolved on the frontend, although it would likely result in a less uniform experience across different front ends (and that might be a good thing, who knows).
Another maybe more theoretical argument for handling it at the blockchain level is that fewer active proposals means less computation. But I don't think this is something that's likely to cost too much computationally, from what I remember.