In my opinion, this is an absolutely terrible proposal. I do understand the rationale behind it, but I feel that this is ill-timed at best.
Right now the PEAR group is in disarray, there is no QA team to speak of, and the single biggest BC break in PEAR history is being forced down the throats of PEAR developers and users alike. The proposal is unbalanced, making zero mention of the effort needed to update packages, nor the problems involved in doing so. Instead, a rose-tinted view of the "advantages" of prefixing is showcased, along with a few meaningless variations of the prefix. In my opinion, this is a recipe for disaster.
Why not let PEAR be PEAR and discuss prefixes in the context of the sorely-needed PHP 5-only PEAR 2.x planning?
Until then, this and any other proposals to force a prefix on existing packages will get my -1, and I flatly refuse to implement it for any packages for which I am lead.