It's been suggested many times in the past.
Are you going to make one of these compilations? If so, are you prepared to support it for several years? Because if people use your modpack and you don't maintain it properly they will be unhappy with you.
Now getting author permissions is not as easy as you think. most authors actually want REAL credit for their work - not just a mention in the credits of the mod - which doesn't count toward their own download count - but toward yours. Just saying I give full credit to Joe Shmoe for this mod is like saying I took Joe's work and now I get the credit. Many authors will just refuse.
Then - if there is a bug that shows up in one of the mods in the future - Will you be willing to redo the modpack? If not it will die a very noisy death as the users trash you for not supporting it. Otherwise, you will be responsible for incorporating any and all changes - experience shows that you will be releasing a new version about once a week or more. Are you willing to spend the time and effort doing that? And you are updating just once in a while how many are going to stick with it?
Now how about size - just how big do you allow this modpack to be? There is a point that it becomes just too big to work with. If it takes over an hour to download on a normal connection - just how many times are you willing to spend the time to upload, then download your compilation to check that it is working? The answer I typically get is you will split it - and now you are responsible for two uploads, and two downloads each time there is a change.
What if someone wants to use a mod that is not compatible with one of the mods in your pack? Do you make a new modpack just for them? or are they SOL?
How about someone that doesn't want one of the mods - is there a way to disable just one without scrapping the entire thing?
Then someone wants a mod that is not in the pack - and the load order is all wrong. They have a choice - not use that new mod, or scrap the pack and redownload each and every mod and reinstall them and work with the mod order to get things to work again.
There are lists of mods along with a known working load order already. They are rarely maintained beyond two or three updates because the owner gets frustrated and abandons them. The frustration comes from stuff like: "Can you add this mod pleeese???" and, "I don't want this mod it sux. If you take it out I will download your compilation - if you don't do what I want then I will not endorse your mod."