A picture is worth a 1000 responses. Seriously, it really helps.

But without the picture, furring out the 2 x 4 portion to be flush with the 2 x 6 portion is not a big a deal. DISCLAIMER: I'm making this statement without having seen a picture.

My guess is that the insulated section closed up an old doorway. The (badly done) framing is very different from the rest of the wall to the right. Could that have been an exterior door and the dining room added on later?

The question now is: What will you be doing there (cabinets, counters, etc.)?

So if I'm following along, the exposed wall is coming down. The cabinets along the window will be straight run into the other room?

Have you checked to see if that is "nailer"? A piece of 2x used so there was something to fasten the drywall to in that corner on either side?

Yes the intent it to run straight across the back wall of the house crossing from kitchen into dining room with cabinets and counters. There is a sliding patio door in the dining room we're reframing to be a window to match in size the one pictured in the kitchen. The dining room is just barely 9' across and it is original to the house. Other homes in the neighborhood have the same layout with the tiny dining room.

We should be dismantling the base cabinets tomorrow and moving the cooktop over to the temporary kitchen area.

That should expose whats closer to the foundation.

We can remove the sheetrock between the window and that exposed too if need be.

We can see everything in the trusses from the ceiling....we opened the entire ceiling in the dining room already when we had to pull ventilation across.

My best guess from what I've seen so far, is that that was framed that way so that drywall could be fastened in the corner. Those random 2 x4's, insulation and plastic is a mess and I highly doubt any of that is original Someone, for some reason, at some time, opened that wall and "stuck" that stuff in there. It will be interesting to see if the plane change continues all across the dining room wall or is limited to that corner.

I have another question. That window wall is is very, very thick. What is the exterior of your house?

We know it's 2x6 across the dining room to the end of the house and also 2x6 from the back to front of the house on that side as the patio door is framed out for 2x6 and the window along the adjacent wall is also 2x6. Ironically it switches back to 2x4 at the front of the house again.

We know the rest of the kitchen (to the left of the window) is 2x4 because we had opened the wall there.

Yep you caught that wierdness too. They built a bump out window...it's not a bow window...It does NOT extend to the ground and the bump is about 14" deep.

The exterior of the house is a fiber type board that is painted. It's not clapboard and not cement board. Something they use on the west coast...never saw this stuff back East

In looking at the original plot plans for when the house was built it looks like the piece of wall between the dining room and kitchen (the part that has insulation and vapor barrier) was exterior facing... Black lines on picture are the original build plans, red lines indicates the builder squared off the corner of the dining room during construction (exists this way today), but left the wall separating the dining and kitchen alone, that explains the insulation and vapor barrier on the partial wall. This change, I'm guessing occurred sometime during or after the wall separating the kitchen from the dining room was built...

You can see the change in the exterior wall. The line of sight will change from 2x4 to 2X6 walls which presents an issue for running a counter and backsplash across the back of the house... how does one hide the transition in wall depth when the backsplash is going across that wall...

As above. Add two inches.

Pretty simple add 2 “ and the cabinets should not have been ordered yet I hope since the kitchen was not ready for design until this is dealt with.