Are you replacing the flooring? That will be needed if you open the wall totally. In this case because it’s a narrow dining room there’s not a lot to be gained by fully removing the wall. The gain versus effort eg new flooring, additional building costs just isn’t there.

They are replacing the flooring in the kitchen and plan to bring it into the dining room. The carpet will stay in the living room

I assume the kitchen is around the corner. Does your mum want to open up the kitchen wall to the dining and the lounge as well and have one big open space? Or just the kitchen/dining wall?

I would look at the roofing structure first, and your (their) budget and see what walls are load bearing. This may dictate how many or how much of the wall is removed.

Also if opening up the kitchen as well, which would be wonderful. How do your parents live. If they have a very clean uncluttered space, then go for it. but if they need to keep the kitchen out of sight, then that is the answer as well. by your photos, it appears it is a neat well kept home....so open it up. I'm with your Mum.

Unfortunately how the kitchen is laid out it needs to remain closed off to the dining (would be awesome if they could open), the kitchen is small and has top cabinets on the wall, they would loose to much usable storage if they got removed. Yes very clean, I have realised that downfall in my open plan house, drives me bonkers 😀

I’d like to see floor plan to get better sense of space

attempting to remove the whole wall to the sides and the ceiling will create extra problems with the structural support and need ceiling, wall and floor patching and not add any additional space..so you need a quote for all the work to help decide the best option easiest most cost effective choice would be to square off the arch without any structural changes

Look at a house that Three Birds Renovations did up where they kept the archway and it looks great. If you're not opening up the space bit keeping 2 separate rooms consider keeping it.

I had a similar archway, which I got squared off. Very little cost to get this done, and floor coverings didn't have to be changed. It was amazing what a difference it made to the look and also how much extra light came through. The three birds renovation was a different situation as they had a brick wall to content with. It is so easy to knock out plaster curves.

Opening it all the way up gives more flexibility, such as if you have an extension table at full length for a big family dinner

The bottom photo here shows the gap opened to the ceiling. It would have looked nice if we could have opened the wall completely but then would have had to match the flooring in both rooms and there would have been less furnishable wall space in the lounge.

Arches are in vogue again so I would do what the 3 birds did and paint and look at updating window dressing to white shutters and even change flooring from carpet to timber or something similar to Karndean planks, this will update the rooms

To be fair Janice in Perth -- your place looks nice , but also a lot more modern . Your place looks like it has no architraves or skirting boards , it has more modern windows , no frames around the windows , etc , etc . That is why opening to the ceiling works in your place IMO , but barring an interior rebuild , this house of Jenny K's parents is always going to look 'of that certain era' .

And whilst I am undoubtably weird , i suspect i will never 'embrace' an arch ( is that why they are called arch enemies haha ? ) no matter whether it is supposed to be en-vogue or painted white

Hi Pottsy99. The house in the photos was built in the 1980’s.

Perhaps the decor makes it look maybe a bit newer?

The skirting boards and architraves have been painted the same colour as the walls so the don’t really stand out.

Hi Jenny, we had an almost identical situation with a second archway as well going into the kitchen. While we were having other work done some 15 years ago (removing a wall) we had the builder remove the arch and square up the passage between the lounge and dining room. The builder suggested that the size of the opening should equate to a set of standard double doors if you ever wanted to add them at a later date. While we haven’t added the doors extra bit, the side wings give some separation between the rooms while still opening up the area. It enables you to put cabinets or other furniture neatly tucked in the dining area. It works and we are very happy with the result. PS we did not take it up to the ceiling.

I would definitely remove the arch.

Can you add a pic showing door to kitchen. if you take to roof you will see top of that doorway.

Looking at the windows, having it finish at the same height would work with them if you cant get a beam hidden fully in ceiling.

Compromise!
Remove the wall on exterior side completely to ceiling...run cornice all the way along that wall/ceiling join...so that wall is all flat (one wall)
Square up the wall to ceiling on light switch side and cornice around the square...remove arch completely, gib the ceiling flat/ remove cornice along the stretch where arch was.
If you are changing the flooring in the dining area to match kitchen..it will be defined as a separate space then to lounge room anyways...so opening walls totally up will not really achieve alot.
This way no electrical switches have to be moved etc and keeps little privacy from kitchen door, adds a little interest to space...I can't see the arch wall as (being load bearing may be wrong), but it looks to be a pretty compact home.
Good luck with decisions!

Example

I just squared my arches off, so that there is still a plastered piece across the top. Like the person who was recommended that double doors could be put there at a later stage. I also personally dislike arches whether they are in vogue or not.

Transitioning fooring between kitchen and dining with Arch and perhaps adding softer chairs to the dining would be easier and money well spent

Getting my arches removed was inexpensive. Only a few hundred dollars.

Personally I love arches, but it will be difficult for it to not look dated without a full makeover. I like Lulu’s suggestion but also suggest getting rid of the verticals as they are an even bigger contributor to dating the place than the archway. Good luck with the decision :)