Elinor does not take that outburst of Marianne's with any seriousness, so I should say that she knows, of herself, that her heart is as feeling as Marianne's. Since Marianne could not be cordial to someone lacking in taste, I suspect she could hardly be affectionate to her sister if she really thought Elinor the equivalent of John for selfishness! *chuckles*

By my lights, if John were 'practical', he would never have mentioned a word about his plan for the fulfillment of his promise, until it were done. Fanny's overreaction to such a simple act should have been transparent to him at once. His sister's (and his step-mother's) plights should have been obvious to him.