IndustrialCraft, EnderIO, and many more mods are updated either to 1.9 or 1.10 (according to CurseForge). I don't see an update for the CoFH mods anytime soon sadly, and there are lots of new mods such as E-Flux by Elec, which supports 1.9 and probably 1.10 as most mods that support 1.9 support 1.10. The mods that haven't added 1.9 or 1.10 support (and are well known mods) usually have replacements for those versions (i.e. Applied Energistics is replaced by Refined Storage and Correlated Potenialistics). In other words, mod developers and modpack makers are trying to get 1.10 as the next stable release that will last a while, much like 1.7.10.
EDIT: "Do not ask, demand or pressure creators to update content, this includes asking if/when there will be an update, and applies well for downgrades" This is the first rule in the Mapping and Modding rules. OP, you kind of broke those rules
With that said, I think this thread should be locked.
I would like to downgrade some mods myself, but I'm still just aning to Java, so it probably won't be anytime soon. Probably the first mod I'm going to backport is Roots, Roots 2 or Embers, because I want to prove elucent wrong that any of his mods aren't going to be for 1.7.10. He decided to use MIT license, not me, so I can do whatever I want with it.
There are lot's of mods that may never be downgraded. For example Gany's mods and M&B: Battlegear 2. Gany's Mods are most likely not be updated because Gany's Surface adds MC:PE beetroot,, and having 2 types of Beetroot (one from vannila and one from Gany) would be weird, and if one mod from Gany's mods isn't going to be upgraded, then other mods won't be updated too, and M&B adds 2nd hand, which is also one of the features from 1.9. I actually find it kinda funny and ironic that 1 or 2 people do that 2nd hand thing better than entire company.
Another mod that is most likely not going to be upgraded is TFC, even if they would skip all the versions after 1.7.10 and start making it for the newest version, by the time they would have it done there will most likely be MC 1.20.