But if it is the Dying Detective and John is not in on it, don't you think that the prospect of losing Sherlock will at the least be an opportunity for John to admit how he feels about him a dying cofession? A kiss? A Johnlock moment to remember.

But we had that already in the bomb train scene in S3.E1 where John thinks they’re dying and does the whole ‘best and wisest’ speech. I dunno. I’m sure the writers could pull it off it they wanted. But I think it would be more original if John was the one dying (and in fact, not faking it) in a three garridebs moment, and Sherlock were the one confessing. Also the whole ‘not being let in on the case’ is old by now, and supposedly that last scene in TAB was where Sherlock decided from now on he should include John in his plans?  So if Sherlock were faking a lethal illness and John weren’t in on it, it would be going backwards.

But honestly, it’s all speculation at this point. I wouldn’t put it past the writers to retread stuff.