The current way Python enhancements are officially considered is described in PEP 1.
This wiki page can be used to capture and discuss enhancements before putting them through the more formal process.
For now, put proposals forth here if you want to try and kick them around a bit and get some feedback before writing an official PEP.
About Using Wiki to Discuss Enhancement Proposals
Thoughts here on moving the official discussion of Python Enhancements from email to wiki.
See also PEEPs.
Discussion of Completed PEPs
Once a PEP is complete, altering the document to capture ongoing community input has a very high bar. Here are some PEP "rehash" pages.