Note: traffic increase will probably only be because of Nodes being run at home. Nodes in datacentres are not ISP traffic anyhow.
Short term will not see any significant effect at all on the ISP model/market. It will just be another (small) set of traffic through the ISPs. Doubt any particular ISP/location will see a particularly significant increase in traffic and will go unnoticed. The only noticeable effect might be a few connected to a few ISPs/locations who push their data quota limit (even if on unlimited with fair-use).
As SAFE is adopted then the traffic becomes moderate and probably less than what bittorrent is today, so again the ISPs are not concerned but some may have noted this increase in traffic. Many ISPs will review their plans for more links to ensure they will meet the growth. And some ISPs will try and restrict bandwidth which might affect some to run Nodes.
Also I think bittorrent traffic will decrease in the medium term because it migrates to SAFE and typically will have as much traffic on SAFE as it did have on torrents.
Longer term will see the traffic increase and those ISPs who have planned for any increase in bandwidth needed will see more customers coming over from any ISPs that try and restrict bandwidth. And in some areas with only one ISP servicing them, then its up to the ISP which way they will go and it’ll suck for those who are restricted since they may not be able to run nodes from home.
But history tells us that even the ISPs that try and restrict, they still increase bandwidth in the long term.
So for the ISP market place I predict that they will adapt to any increase in required bandwidth as they have done in the last 20 years. Remember the few MByte per month quotas and 28 or 56 Kbit/sec link speeds? Now in AU we have 100/40 mbit/sec available for many (soon to be most) and I have unlimited quota. Yes 10 to 15 TByte/month does not get me any nasty letters. Not that I do that each month My ISP 13 years ago would send a nasty letter at 3GB a month.
Now comes the question of MESH networks. Will we see the rise of the mesh networks in the next 10 years? Will we see more of the community owned ISPs which will be a combination of mesh/traditional connections? All these will affect the traffic flow and how the market looks longer term. But short term its doubtful we will see this much at all.