Speed cap aside (good point Chrys btw), I would think those that will benefit most are those who perhaps started off at 80/20 but lost speed due to x-talk.
It may also give a bit more to those who were say previously syncing at say 30Mbps on the 40Mbps products.
Re the long lines, I doubt they would 'soak it up' as such. DLM should only attempt the lower target after a period of stability (ILQ green). The longer lines tend to get more errors therefore it would have to be stable green before attempting 5dB. It would also require ILQ green again before going down to 4dB, even if its amber that should cause a no action. If ILQ red, then it should back off.
Time frames for XdB may be different to the INP status - I don't know as I dont have those details, but if it does use an ILQ status similar to INP, then time frames definitely do get extended to stop lines flapping.
For INP I have observations written down somewhere, but from memory its 1 day, 10 days, 14 days and so on. So first time it tries it, it could go down quite rapidly, but next time it will be more cautious.
When they first brought xdB out on the Huawei's I saw mention from a couple of ISP {TT} reps that it may cause problems and increase in fault rates, but that hasn't happened. The ILQ system seems to take care and back off as soon as MTBE goes red. Whilst I appreciate that BS said he saw some errors when it was trying it on his line and he reset DLM himself as mentioned in that thread I suspect DLM would have noticed anyhow and backed off the next day. BS has an advantage that he could reset line himself which takes immediate effect rather than wait until next day to take action.
3dB works perfectly fine on adsl2+ lines without G.INP. It only gives it to lines that are ILQ green. There are plenty that just dont get it at all because their lines are either ILQ amber or ILQ red. Although XdB has been available for quite a while on GEA-FTTC-Huawei, there are still plenty of lines still running at 6dB because they dont meet the ILQ requirements.
