I would rather move more extensions from core to PECL, than from PECL to core.
From my experiences the problem with this is many shared hosts wont install
non core modules, so the more modules moved from core to pecl the less flexible php will be and the less use it will be. I understand the need to keep the core code maintained and as clean and lean as possible, but we also need to look at what developers need to create applications that can be used with mass virtual hosting. Regards Marco