I have seen this feature requested a couple of times way back in the forums, but I would like to know if there are plans to implement it, if it is a difficult feature to implement, or if anyone knows of workarounds.

When I used to edit with Final Cut I had a simple (and relatively common) method to ensure that I never lost any work while editing - duplicating sequences with each 'pass' of the footage:

First I would go through all my footage and insert all potentially useful sections in a sequence called 'MySequence 01' - let's say this sequence is 90min long.
I duplicate 'MySequence 01' and rename it as 'MySequence 02', and then go through a first pass of 'MySequence 02' removing anything unnecessary.
At the end of one pass, 'MySequence 02' might be 50min long. I duplicate the sequence, and start another pass on 'MySequence 03'. and so on.

With duplicated sequences, I know I can make a big change to a scene in 'MySequence 12', edit it all the way to a fine cut in 'MySequence 14', and then decide that, no, the way that scene was cut in 'MySequence 11' was better. Then it is a very simple, very fast change to grab the required clips as they are cut in 'MySequence 11' (before the change was made) and paste them into 'MySequence 14'. No time wasted, no lost work.
This means that I have a lot more flexibility in the edit. This is also extremely useful when working with other people on an edit for them to see which is the most up-to-date sequence and track how the project is coming along.

Currently, using Kdenlive, I have to be very cautious while editing and prefer not to experiment, simply because I know how much time it will cost me to fix edits and sequences that don't work. This is not just an issue for large feature-length films - most of my videos are only 5-10mins long and this is a serious impediment to my workflow. I know that you can import another project as a clip, and I do save projects with incrementing numbers, just in case, but it is not an adequate workaround as the clips, audio and music are no longer separate and editable. The lack of multiple sequences in Kdenlive costs me time and creativity - for a documentary workflow this feature is very, very important.

Does anybody have any news or suggestions on this issue?

Maybe you could just do a select all and copy the edited clips and then paste them as a copy at the end of the time line.
Group the pasted clips together so you can not accidentally disrupt the edit. Then edit the copy that you started with. When you want to render the project use the render select region option to just render the section you want. And if you need to revert any part back you can copy from the old sequence saved at the end of the timeline.

thanks for the suggestion! while not ideal it could be the best option at the moment :)

So like drag a timeline selection whether whole project at that point or just a sequence between in/out points and drag to the project tree as an xml mlt file and ability to save as an mlt file or seperate kdenlive project for possible reuse.

I agree with this request, I worked for long time with pinnacle/avid Liquid wich allowed me to make various sequences in the same project. As I see this is helpful in complex projects, ie. I used to make a sequence with some clips chopped at timeline as a separator sequence and then import that sequence in a new one placing and repeating it at the main sequence timeline. I know this could be done simply making a project for the first seq and then render it and then placing it at the second seq, but having the hability to work on various sequences in the same project sharing the media in those sequences and having the opportunity of make last minute changes at any sequence gives you a great flexibility.
Regards.

For what it's worth; the outstanding request for this - http://www.kdenlive.org/mantis/view.php?id=718