A perhaps more workable solution would be to have per-tab indicators of total bytes downloaded, peak memory used, and total CPU time used (the first one already exists as part of the developer tools, but it's hidden by default). People on fast computers and fast networks do not feel the weight of bloated pages; making it visible to everyone provides an incentive to reduce it.
I really think that you are onto something there. Or maybe a bloat index calculating the ratio between user content and downloaded content. Like 1kB of text but with 2 MB of JavaScript/CSS etc would give you an index of 2000 whereas if you only had 23 kB of JavaScript/CSS etc, it would 23.
