How big is the corner of the dining room (where @titchy put a loo) if you square it off in line with the wall of the kitchen? You only need about 1m width and a bit more in length for a space saver loo and sink combination plus stud walls if you have the door opening outwards.
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I think your idea risks spending a lot of money that will result in 2 irregular shaped, small rooms with lots of wasted unusable space, instead of 1 big and 1 small room, that will look a bit bodged so future buyers' first thought will be that they want to spend money on redoing it, devaluing your home. Whereas swapping the rooms so you have a big kitchen would make the house more attractive to buyers and building a small extension like I suggested or adding a loo would add value. I think you need to get quotes for all the options and weigh them up against how they affect the value/desirability of the house. It would be silly to spend thousands on works that devalue the house when you could get a future return on your money for a few thousand extra, even if that means waiting a bit longer.
My suggestions (in order of expensiveness based on my guesstimates):
Keep the layout as it is but put in pocket glass doors to the kitchen, making it effectively open plan so the size of the kitchen matters less), and move back the hallway wall and replace with another glass pocket door. When you replace the kitchen (not necessarily now), you have just enough room to have units in a U shape. You can add a dresser or display shelves on either side of the chimney breast and window seat cupboards in the dining room for extra storage for crockery, wine glasses, wine storage etc, things that you use in the dining room rather than the kitchen. You could even have a drinks fridge or extra freezer under the stairs.
Move the wall of the kitchen as you suggested and put in glass pocket doors to both the kitchen and hallway. I think that just about gives you enough room for a 6-8 seater table running lengthways towards the window in the middle of the dining room and a window seat cupboard if you move the hallway door (3 feet either side of the table). There will be enough room for sitting in front of the chimney breast. Square off the kitchen and turn the corner alcove bit into a walk in pantry, a desirable feature, so you don't end up with a weird, irregular kitchen and add kitchen cupboards in a U shape, as above. That would add desirability, if not value.
As above, but turn the alcove into a space saver loo opening into the dining room so you don't have the issues of a loo opening into the kitchen and you don't end up with a "corridor" into the kitchen (as in titchy's plan), which makes the extra space you have gained in the kitchen unusable. I think there is just enough room to have the door opening outwards if you also move the hallway wall. A loo would add value.
Swap the kitchen and dining room with pocket glass doors in between. A large kitchen will always be more desirable than a large dining room. You could probably fit in a larger loo like titchy's plan if you did that, with the door facing to the left wall (so not into the kitchen), creating a lobby to the dining area. It's a bit of a waste of space but wall space is more important than floor space in a kitchen IYWIM?
Look at the costs of extending the one storey part of the house to square off the dining room and add in a loo and utility area next to the kitchen (accessed from the kitchen by the current back door). If you can save money by not replacing the kitchen now, you could invest that in something that increases the value of the house. A basic single storey extension costs about £1 - £1.5k per square metre. I don't think it would cost much more to extend all the way to the back of the kitchen than swapping the 2 rooms over (although you seem to have gone off that idea), which would be expensive for no gain in value.