Chronic Kidney Disease (CKD) with Nephrotic Syndrome: The patient's longstanding untreated hypertension, worsening peripheral edema, significant proteinuria (2.8g), and rapid decline in renal function (GFR from 40s to 11) over three years strongly suggest CKD with nephrotic syndrome. The elevated BNP and dilated left atrium on echo also indicate fluid overload and possible cardiac involvement.

Heart Failure with Reduced Ejection Fraction (HFrEF): The symptoms of SOB on exertion, peripheral edema, elevated BNP, and echocardiographic findings of a dilated left atrium are consistent with heart failure. The patient's hypertension and CKD are risk factors for the development of HFrEF.
Diabetic Nephropathy: Although not directly mentioned, the presence of significant proteinuria and CKD in a patient with hypertension raises the possibility of diabetic nephropathy, especially if the patient has undiagnosed diabetes.

Renal Artery Stenosis: Given the patient's longstanding hypertension and rapid progression of CKD, renal artery stenosis should be considered, as it can cause both hypertension and renal dysfunction.
Vasculitis (e.g., ANCA-associated vasculitis): Although less likely, vasculitis can cause rapid deterioration of renal function and should be considered, especially if there are other systemic symptoms.
Obstructive Sleep Apnea (OSA): OSA is common in patients with hypertension and can exacerbate both hypertension and heart failure. It's a "do not miss" diagnosis due to its high prevalence and significant impact on cardiovascular health.

Amyloidosis: This condition can cause nephrotic syndrome and heart failure. Although rare, it should be considered in the differential diagnosis, especially if the patient has other systemic symptoms or if the more common causes are ruled out.
Fabry Disease: A rare genetic disorder that can cause hypertension, CKD, and heart failure. It's more likely to be considered in younger patients but should remain in the differential for patients with multisystem involvement.