The problem with reinventing things is that you now have two or more incompatible mechanisms to accomplish a task, which dilutes the effort, and can confuse the marketplace (should I use X or Y interface, since both seem to be in the CPAN?).
Witness News::NNTPClient, an interesting implementation that predated Net::NNTP, but is now abandoned. I wrote quite a few programs using the old interface, but have finally just recently succeeded in cutting them all over. And I did that because I know that Graham Barr will be around to update Net::*, but who knows about any efforts to pick up the other package.
SImilarly, a solution based on top of LWP will very likely continue to work and get bug fixes, because I know that LWP will continue to be maintained for some time to come. But if japhy submits his independent code to the CPAN, will he notice when Gisle updates LWP for a security fix, and re-implement that? I think not.
So, the code doesn't do as much as LWP, won't be maintained the same way as LWP, and doesn't leverage off the existing code in any big way. Do you think I can recommend this little code for any production work? Hardly not.
Now, if japhy writes code that uses the LWP callback, the codesize will be reduced, everything will play well with proxies and new underlying protocols, and the chances that the code will be maintained will be greatly increased. Everyone wins. I encourage japhy to rewrite the code to use the callback, and submit it. I would not encourage the current code to be submitted.