I had a whole reply that disappeared.. Oh well... short version.
Most people I know mainly watch OTA programming - well, that will still be available regardless of streaming. It might be in the future that the cell phone companies will stream this material for all as well (really only five networks here).
Most of us here are TV watchers - that's why we bought ourselves this toy and was pleasantly surprised at how effective it really is. The DVR changed how we watch TV (as did the VCR, but I think more so in HOW we watch TV). I watch more TV now in less time - especially since most TV is filled filler (coming up on, previously on, recaps, preview, etc.) Heck sometimes American Idol on the result show is shortened in this household to 5 minutes!
If you think about all the programming you pay extra for on cable/satellite, there is lots of cross pollenization. The Discovery/TLC/History/DIY/HGTV/Food/MTV/VH1 networks probably only put on 3 hours of programming a day - the rest is either repeated, chopped and recut, old stuff, or even shows from its' sister networks that show up on it. The Science Channel is almost all Discovery shows recut from the past, and some of the other stuff is shows from Canada. When you narrow it down, some of these channels are less than a $1 per household for the satellite/cable companies - so what value are you REALLY getting?
I would hope in the future some of these shows would just be the new material - I would much rather watch a 15 minute reality show without filler than an hour one - and since you aren't subject to marketing/ratings with lead-ins and time slots that destroy otherwise good shows that monkey with its' position and audience - I think we might get better programming. Shows in England run real short sometimes - they explore their premise and end it. The Young Ones - groundbreaking an hilarious - 12 episodes (or something like that). Fawlty Towers, The Office, Spaced, etc. They don't beat the dead horse over there nearly as much. If we didn't have a grid system on TV and actually had choice to what we want to watch WHEN we do - I think our entertainment landscape would change drastically. You wouldn't have to worry about when 18-35 yr olds are watching - they are watching whenever they want! Same thing for a show that has a more mature content (sexual or otherwise)... it can just be out there and not stuck to after 10pm.
I think the Roku (and its' competitors) could really change the face of media - and in a good way. Traditional TV could still be out there, but it would be tied into a DVR and the internet streaming box. Most of your big budget stuff still on the major networks - your other shows could be out there in cyberspace.
As for the network bandwith issue - stop getting tied up with technology - new technology is always being developed to solve a need. That's how the wheel got invented. Crap, 10 years ago who would think we would have full web and application access via a phone. 10 years before that, texting and email via cell phone - let alone a digital connection would have be stuff to dream about.
Even 20 years ago, you would have had to have a university and a text terminal for us to debate this crap like we are, and 10 years ago, video on the internet at all would have been abysmal at best.