A "master" merged playlist.

[deckoff]

I hope I  would be able to clearly explain what I mean.
So, how about every account gets "master" merged playlist, with static web address. Now, to get a few playlists merged, one would have to upload all the playlists he needs merged ad merge then one with another. If a playlist address is changed, a playlist has to be omitted,   the process should start from the beginning.
What I suggest is:
One "merged" playlist, with static address, for each account. An option to select witch of the  playlists you have uploaded you want go be "merged" into the "merged" playlist. 
So , for example, one has playlists Aaaa Bbbb and Ccccc. with address http://Aaaaa , http;//Bbbb and http;//Ccccc. Each uploaded playlist is accessible with its own address ( like now) 
The merged playlist has the interface to select whcih of the playlist you want, you have in. So , you can have a feed with all 3, or only Aaaaa and Ccccc. If you decide to upload a new one, say, Ddddd, and dont need Bbbb, it will be much easiler to delete the old, upload the new, and select if you want it in the merged or not. 
Another benefit for some users will be, that once the address of the playlist is added, it wont have to be changed after each change.
Remember, Kodi does not support copy/paste   
Hope I am clear, and the post is not tl

[Epg Admin]

You can merge m3u files right now, but of course if you merge two files, the second one gets deleted.
You can also choose which url you want to keep by merging the files you don't want to keep with the file you want to keep.

So if you want to keep the link of Aaaa then you click the merge button next to the Aaaa file and say "merge with Bbbb". Then the Bbbb file disappers with its link and the data will be added to Aaaa.

If I understand you right, you want to keep the files Bbbb and Cccc even if you merged them with Aaaa.

Is that correct?

[deckoff]

You can merge m3u files right now, but of course if you merge two files, the second one gets deleted.
You can also choose which url you want to keep by merging the files you don't want to keep with the file you want to keep.

So if you want to keep the link of Aaaa then you click the merge button next to the Aaaa file and say "merge with Bbbb". Then the Bbbb file disappers with its link and the data will be added to Aaaa.

If I understand you right, you want to keep the files Bbbb and Cccc even if you merged them with Aaaa.

Is that correct?

yes
Exactly that. Keeping all the playlists separate, AND getting a merged playlist at the same time. Also, this will allow to easily change which playlists will be merged.
Should be useful for people that might want to change the source of one or more of the playlists they have. I assume managing updates of more than one playlist will be easier.

[Epg Admin]

We looked at it and we decided that it would be too confusing and unnecessary.

You can clone an m3u file and you can merge the clone in the master m3u, keeping the original.