Leveling uneven kitchen walls for porcelain tiling

[Poiup]

I will be tiling with 60*30 procelain tiles. They weight about 3.57kg each which is about 20.6kg/sqm
The wall is not flat and it's plastered. Then ripping the current tiles off, some of the plaster also came off and when doing the "coin test" I can feel that some bit of plaster are not sound.

Considering all this I think that tiling over the existing plaster is a no go. How can I solve the situation?
I was thinking about doing the following:
1) in the area that will be tiled, chisel away the unsound plaster exposing the sort of mortar underneat. Leave everything as is where I will not be tiling... the kitchen units will cover that area anyway
2) install sheets of 6mm hardiebacker in the recessed areas where I will be tiling
3) install all the kitchen units and then tile over the hardiebacker

Do you think this would work? Any other idea?
I know I could just use plasterboard instead of the hardiebacker but it would be ticker and I don't know if that thickness would be excessive. Any advice?

 

[Wayners]

Knock all the plaster off. Get it skimmed flat.

You could cover entire wall with backing board stuck on. Wedi washers and screws

 

[Poiup]

Knock all the plaster off. Get it skimmed flat.

You could cover entire wall with backing board stuck on. Wedi washers and screws

I've attached a few pictures of the wall as it is at the moment.
Behind the plaster there's something like bonding. I suppose that I don't need to remove?

I thought that my best bets are to either:
-somehow flatten by skimming, but I can't do it with plaster because of the tiles weight issue AND I don't intend to wait 3/4 weeks for it to dry. What product could I use for that?
-create a recess just where the tiles are going to be and add a layer of hardieback just there (however, I would probably need to put some sort of leveling compound behind it because there's no way I can create a flat and uniform recess. Again... what product could I use for that?

 

[Wayners]

Need to sort cables as can't go diagonal.
Is plaster loose then?

 

[Poiup]

Need to sort cables as can't go diagonal.
Is plaster loose then?

If I tap over it with a coin, plaster is loose in some areas and seems OK in others.

 

[Wayners]

If you screw backer board over it will be fine.