As to constant bandwidth/covertraffic, that is expensive even today. For constant bandwidth to get a 5 second response time for a smallish say 3MB web page you need to have 3 MB of covertraffic every 5 seconds, or 50GB per day, per link. Ouch.
I thought about this a little bit, and the concern doesn't add up to me. As a consumer and participant in small businesses, I've only ever seen bandwidth that is metered per availability, not per use. The price is the same whether I use it or not. The amount of bandwidth available to a set of people who stream videos with or without filling the downtime with cover traffic is exactly the same. A low-end consumer link that provides 1MB/s bandwidth does indeed provide 84GB of transfer every day. The idea of constant bandwidth could of course be extended to manage changing bandwidth conditions without providing for timing correlation, so long as the use of the bandwidth is unrelated to the actual requests, it could have any arbitrary shape to fit within availability.