Unfortunately adsl is not really designed to cope with this amount of bandwidth. The exchange backhaul simply cannot cope - never mind the ISPs.
Each MSAN has a STM-1 155Mb optical fibre link for the backhaul (orange fibre in pic below).
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Doesnt matter of youre on IPStream.. or with an LLU provider.. but that link from the MSAN is going to be holding up to 2000+ users.
Some of the older DSLAMs work a little differently.. you still have the 155 backhaul limitation.. but the backhaul is segregated into several VPs - and although there may not be as many users, its not unusual for VPs to only say have 20Mb allocation.
Either way its not going to take too many users running at full pelt before contention kicks in.
ADSL was originally designed as a cheap way for users to get broadband, by sharing the cost and the amount of available bandwidth. With a leased line sure you can max it to the full whenever you want.. but the cost of several thousand per month is too expensive for most.
Its one thing increasing speeds, but if users are going to be doing more and constant streaming is using up that bandwidth then things could start to crumble.
ADSL relies on traffic being bursty and not too many packets being requested at the same time for us to all be able to share the bandwidth.
Below is the official BT definition for the use of adsl
... the End Users require occasional fast but ‘bursty’ access to private network facilities and / or the Internet (via the Customer). The products are not suitable for End Users who require continuous bit-rate, full bandwidth services.
In other words it just wasnt designed to allow high rate continuous streaming
